Hanover-York District Pennsylvania
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UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGY OF THE HANOVER-YORK DISTRICT PENNSYLVANIA
GEOLOGICAL SURVEY PROFESSIONAL PAPER 204
CONTENTS V Faare PLATE 10. A, Polished surface of recumbent fold in albite-chlorite-muscovite-quartz schist, 7 miles northwest of Tucquan anti cline; B, Fold in albite-chlorite-muscovite-quartz schist; C, Muscovite-chlorite-quartzs chist, from Muddy Creek Forks; D, Albite-muscovite-chlorite schist, from Fenmore ______41 11. A, Muscovite-chlorite schist with quartzose lenses; B, Coarse-grained albite-chlorite-muscovite schist; C, Gra phitic quartzite- ______48 12. A, Marburg schist, three-quarters of a mile north of Craley; B, Marburg schist, 1 mile north of Windsor; C, Marburg schist, from Marburg______48 13. A, Marburg schist, 1 mile north of Marburg; B, Marburg schist, showing greater detail; C, Quartzite associated with Marburg schist, 1}_ miles southeast of Dallastown_--__-______-_--___-_--_-__-_----__--_---_--___ 48 14. A, Chloritoid-muscovite-quartz schist, from Saubel Hill; B, Chloritoid-muscovite-quartz schist, from Hoffacker Valley; C, Banded chlorite-muscovite-quartz schist, half a mile south of Freysville______49 15. A, Foliation layers in garnetiferous chlorite-muscovite schist; B, Garnetiferous chlorite-muscovite schist; C, Quartz pebble in conglomerate near base of New Oxford formation, cut through and slickensided by fault plane; D, Garnet crystals in solution pockets in metamorphosed conglomerate in the Gettysburg shale______56 16. Sketch map of Triassic sedimentary racks in western New Jersey, Pennsylvania, and Maryland, showing diabase sills, crosscutting bodies, and dikes--____--______-______-___-__---_-_--_------_---_--__---_--__ 57 17. Map of the Hanover-York district and adjacent region, showing major structural axes and thrust faults north of the Martic overthrust_---__-______-______-______--____-__-----__-__-__._--__ 64 18. A, Mylonitized Chickies quartzite from sole of Highmount thrust fault; B, Harpers phyllite thrust northwestward over Ledger dolomite; C, Polished surface of closely folded quartzose Harpers phyllite- ______68 FIGURE 1. Index map of southern Pennsylvania and adjacent part of Maryland, showing location of the Hanover-York district. ______1 2. Map showing physiographic divisions. ______3 3. Columnar section of sedimentary rocks north of the Martic overthrust in the Hanover-York district.______7 4. Geologic map of gorge of Codorus Creek north of York______10 5. Sketch of section of Chickies slate south of Violet Hill______12 6. Sketch of section of Chiekies slate on east side of Mill Creek, south of Plank Road______12 7. Sketch of section of Chickies slate east of Codorus Creek near York Country Club______-_-__-_-__-___ 12 8. Geologic sketch map and section of the limestone north of Wrightsville._____-_--_____----__-_-_------_--_ 21 9. Geologic map of northern part of York.______-__-_____--_-___-_------_ 22 10. Geologic map of West York and vicinity______-______--_---_------_--_---_-__ 23 11. Sketch of plan and section in quarry of Universal Gypsum & Lime Co. in West York______24 12. Sketches showing dolomitization of limestone in quarry of Universal Gypsum & Lime Co. in West York______24 13. Sketch plan and sections in abandoned quarry of Palmer Lime & Cement Co. in West York______25 L4. Sketch of plan and sections in quarry of York Valley Lime & Stone Co., 6 miles northeast of York. ______26 15. Sections of A. M. Hake quarry in York______-__-_------^------__--_- 28 16. Sections along Codorus Creek at Eli Zinn quarry in southern part of York______-_-_-___---_-----___ 29 17. Section along Dover road over Glenmount Cemetery Hill.____-_--______31 18. Sections in Roy Bittinger quarry west of Spring Grove.______-____--_---_---_-_-_-_-_--- 31 19. Sections of folded Conestoga limestone in William Grothe Brick Co. clay pit, southeast of York______35 20. Geologic map of eastern part of the Gettysburg quadrangle. ______-_____-_-_-__--__-__---__ 38 21. Sections of Marburg schist and associated quartzites at Brodbeck______-______--__-----_-_-----_- 44 22. Ideal progressive sections across the Triassic basin, illustrating hypothetical mode of deposition of the sediments. 54 23. Sketch of plan and section of the Gnatstown overthrust exposed in a small quarry on Pottery Hill southwest of York______61 24. Revised geologic map of the Mount Zion and Accomac anticlines in the Middletown quadrangle__-____-______61 25. Theoretical restoration of folds of the Hellam Hills anticlinorium before overthrusting.______'_ 63 26. Map of southeastern Pennsylvania and adjacent part of Maryland showing relationship of general structure ______65 27. Sketch map of the Hanover-York district and adjacent areas, showing the structural axes in the Martic overthrust block______--______-__-_ 69 28. Map of normal tension faults in the Hanover quadrangle and adjacent part of the York quadrangle.______74 29. Sketches of faults in quarries northeast of York_-______-_--_---___--_---__--__-_------_- 80
ABSTRACT
The Hanover-York district includes the Hanover and York faults, and that remnants of the eroded Glades thrust block lie quadrangles and the Pennsylvania portion of the Westminster on limestones of the valley northwest of York. and Parkton quadrangles. The district is in York County ex The Stoner overthrust on the south side of the Hanc^er- cept a narrow area in Adams County on the western edge of the York Valley in large part has overridden the Strickler anti Hanover quadrangle. The largest cities are York, the county cline in the northeastern part of the district and has cut off seat of York County, an industrial city of about 75,00 inhabitants minor folds in the syncline to the southwest. near the north edge of the district; and Hanover, near the south Normal transverse faults trending north to northwest off west border. Both cities are located in the southwestward- set the basal beds of the Triassic sedimentary rocks and are, trending Hanover-York Valley, which crosses the district. This therefore, of Triassic age. Related normal faults are probably synclinal valley is underlain by Lower Cambrian and Ordovician also Triassic. Other normal faults break up the Glades ever- (?) limestones and dolomites from which is derived most of the thrust block but do not; affect the Triassic rocks. Such feults mineral wealth of the district. The valley is bordered on the are believed to be pre-Triassic and to have resulted from the northwest by the Hellam and Pigeon Hills, anticlinal uplifts fragmentation of the moving thrust block. that expose pre-Canibrian volcanic rocks and overlying Lower The southeastern part of the district, which lies southeast Cambrian conglomerates, quartzites, and phyllites. The Pigeon of the closely folded lower Paleozoic limestones and dolomites, Hills, which attain an altitude of 1,220 feet, are the highest is an upland area containing crystalline schists of the Glen- land of the area. Lower Cambrian arenaceous rocks are about arm series. The schists are largely argillaceous and arena 2,000 feet thick in anticlines north of the Hanover-York Valley. ceous in character and include mica schist, quartzite, volcanic Other anticlines of these Lower Cambrian rocks lie south of the flows and tuffs, and some marble. These rocks are not litho- valley, but the conglomerate beds near the base are exposed logically equivalent to the lower Paleozoic limestones and dolo only near Mount Pisgah. The Chickies quartzite, which is a mites, and the contact between the two series is one of dis white quartzite north of the valley, changes to «. slate facies cordance caused by faulting along the Martic overthrust. No fos with thin quartzite beds south of the valley. The anticlines of sils have been found in the schists, and they are assigned a Lower Cambrian arenaceous rocks plunge eastward into the probable pre-Cambrian age. East Prospect syncline, a valley on the eastern edge of the dis The schists are described in detail, and thin sections of them trict underlain by Lower Cambrian and Ordovician (?) lime are illustrated. Folding and metamorphisni took place over a stones. The valley continues eastward into the wide Lancaster long period and metamorphism is of variable intensity in dif Valley. ferent parts of the Martic overthrust block. The metamorpl ism Triassic rocks, largely red sandstones and shales, cover the is largely paracrystalline with the folding and, in part, outlasted northwestern part of the Hanover quadrangle and form an up it. Recumbent folds are observable in the schists, especially land of low relief, which is part of the Gettysburg Plain. in the vicinity of the Tucquan anticline, which crosses the south The basal beds overlap the limestones of the York Valley and eastern part of the district. The most prominent structure, older rocks on the north side of the Pigeon Hills and dip gently however, is the foliation, which resulted from the shearing out northwestward. A diabase sill and diabase dikes cut the Trias of the closely packed recumbent folds. Consequently, the present sic sedimentary rocks and also the older rocks to the south superposition of layers is not a stratigraphic succession. The east. recumbent folds may reflect, on a small scale, a large recum The lower Paleozoic limestones with the underlying arenaceous bent fold developed during the movement that superposed the rocks are a part of the Paleozoic carbonate sequence of the Great Glenarm series on rocks of known Paleozoic age; and the Valley. The Lower Cambrian limestone and dolomite in the displacement may have taken place by a large-scale recumbent Hanover-York district is a fossiliferous series of beds equivalent fold. The foliation, resulting from the shearing out of earlier to the Tonistown dolomite of the Great Valley, and belongs to a folds has been deformed by the latest compression, which has different sedimentary facies that was deposited in the southeast folded both the rocks of the Glenarm series and the overrid ern part of the main Appalachian geosyncline. den Paleozoic rocks lying to the northwest. This folding is The lower Paleozoic strata and the underlying i>re-Cambrian known to be post-Beekmantown in age and is probably late rocks are closely folded and broken by thrust faults along which movement was northwestward. The southern anticline of the Paleozoic. Pigeon Hills was thrust across the northern anticline, the move The chief mineral resource of the district is limestone, which ment taking place on the Gnatstown thrust fault, which extends is obtained from many large quarries in the valley near York and along the valley eastward to York. A restudy of the structure Thomasville and is burned for lime, ground for agricultural use, of the Hellam Hills in the Middletown quadrangle has shown or crushed for road material and concrete. Clay derived from that the Highmount and Glades overthrusts of that area, which the weathering of impure limestone is used for brickmaking, and extend into the York and Hanover quadrangles, are thrust sand is dug for local building purposes. VII
GEOLOGY OF THE HANOVER-YORK DISTRICT, PENNSYLVANIA
By ANNA JONAS STOSE and GEORGE W. STOSE
INTRODUCTION of the Continental Congress. It is now an industrial LOCATION OF THE ABEA city of about 75,000 inhabitants. Hanover, also a city that dates back to colonial times, is at the southwest The area covered by this report embraces the Hanover end of the York-Hanover Valley. The population of and York quadrangles in southern Pennsylvania, be Greater York was nearly 75,000 in 1940.1 The popula tween parallels 39°45' and 40° and meridians 76° 30' tion of the boroughs of West York and North York and and 77°, and includes also a narrow belt 2 miles wide of Spring Garden and parts of West Manchester and
76'00'
•Lebanon LEBANON
CUMBERLAND Breeches
C A F! R O L L
11 Westminster Belair Havre de • Grace
FIGURE 1.—Index map of southern Pennsylvania and adjacent part of Maryland, showing location of the Hanover-York district. just north of the Maryland line in the Westminster and Springettsburg Townships are included in this figure. Parkton quadrangles, which lie directly south of the The population of the city of York in 1940 was 56,712, Hanover and York quadrangles respectively. The area and that of Hanover was 13,076. Other towns and vil therefore is referred to as the Hanover-York district. lages in order of population are: Eed Lion 4,891; D^.l- The greater part of the area is in York County, and lastown, 2,917; Glen Kock, 1,412; Spring Grove, 1,259; about 20 square miles along the west side of the Hanover Windsor, 1,108; Stewartstown, 985; Shrewsburg, 720; quadrangle is in Adams County. (See fig. 1.) Yoe, 528; and Jefferson, 400. The population of many York and Hanover are the largest towns in the dis other villages is less than 500. trict. The city of York, the county seat of York County, 1 Information on population was furnished by the Chamber of Om- was founded in 1741, and in 1777 was the temporary seat merce, York, Pa. GEOLOGY OF THE HANOVER-YORK DISTRICT, PA.
The central part of the area is crossed by the Balti No. 178, 1926. Geology and mineral resources of the more and Harrisburg division of the Pennsylvania Rail Lancaster quadrangle, Pa.: Idem, No. 168, 1930. road, which follows Codorus Creek to and north of York. Knopf, E. B., and Jonas, A. I., Geology cf the Mc- A branch extends east of York to Lancaster and another Calls Ferry-Quarryville district, Pa.: U. S. Geol. Sur runs southwest to Hanover and Gettysburg, with a vey Bull. 799,1929. branch by way of Littlestown to Frederick, Md. The Stose, G. W., Geology and mineral resources of Western Maryland Railroad extends from York through Adams County, Pa.: Pennsylvania Topog, and Geol. Spring Grove to Hanover and has a branch line up the Survey Bull. C-l, 1932. West Branch of Codorus Creek into Maryland. A bus Stose, G. W., and Jonas, A. I., Geology and mineral line runs along the valley from York to Wrightsville, resources of the Middletown quadrangle: IT. S. Geol. and an electric railway runs from York to Spring Grove Survey Bull. 840, 1933; Geology and mineral resources and to Hanover. of York County, Pa.: Topog. and Geol. Survey Bull. C-67,1939. PREVIOUS WORK Although both authors covered the entire area in the field, the writing of parts of the report was divided. The earliest geologic work in the Hanover-York dis Anna J. Stose wrote the part relating to the pre- trict was that of the First and Second Geological Sur Cambriaii rocks, the rocks of the Martic overthrust veys of Pennsylvania. The results were published in block, and their structure, while G. W. Stose wrote most reports on York and Adams Counties. In reports of the of the geology and structure of the Paleozoic and the Second Geological Survey Lesley and Frazer termed the Triassic sedimentary rocks and prepared iiost of the rocks, older than the limestone, gneiss, hydromica schist, phyllite, slate, and Cambrian quartzite. The limestone accompanying structural diagrams. was called Silurio-Canibrian, and the Triassic rocks ly The writers wish to express thanks to K. E. Lohman, ing northwest of these older rocks were recognized as of the Geological Survey, for the photomicrographs "New Red" sandstones. Walcott 2 reviewed the earlier figured in this report; to C. E. Resser, of the U. S. work of the Pennsylvania Geological Survey and de National Museum, for determination of the fossils; and scribed Lower Cambrian fossils in the quartzite 4 miles to E. B. Knopf, of the Geological Survey, for assistance northwest of York and in limestone at several localities and helpful suggestions on the metamorpliic and struc in and near York.3 Most of his fossil localities in lime tural problems of the Martic overthrust block and of the stones are now covered by York city development. Wal adjoining metamorphosed Paleozoic rocks. The photo cott concluded that, excepting the Mesozoic sandstone, graphs, except those of polished rock specimens, which no rock in York County is younger than Lower were made in the photographic laboratory cf the Geo Cambrian. logical Survey, are by G. W. Stose. SURFACE FEATURES FIELD WORK BY THE WRITERS AND ACKNOWLEDGMENTS SURFACE FORMS AND ALTITUDE Field work on the area here described was started The Hanover-York district is part of the physio in 1920 when the authors made a reconnaissance of the graphic division of the eastern United State? known as valley limestones from Hanover to Quarryville in order the Piedmont province. (See fig. 2.) The surface to establish the lower Paleozoic section of the region forms are of four distinct types: (1) A well-dissected and to correlate the formations of the Hanover Valley upland in the southeastern part of the area; (2) The west of Hanover in the Gettysburg quadrangle with Hanover-York Valley, a narrow lowland tl at diagon those in the valley to the east. The area was mapped ally crosses the area; (3) High hills and peaks that form in detail during parts of the field seasons from 1922-37. the Pigeon Hills and the southern part of the Hell am The work was done in cooperation with the Pennsyl Hills; (4) A dissected low upland northwest of the vania Topographic and Geologic Survey, G. W. Stose Pigeon Hills, part of the Gettysburg Plain. representing the Federal Survey and Anna Jonas Stose The southeastern upland covers about two-thirds of the State. Previously published reports on quadrangles the Hanover-York district. (See pi. 1.) It includes * to the east, north, and west of the Hanover-York dis parts of four drainage basins, the largest of. which trict are as follows: drains northwestward by the three main I ranches of Jonas, A. I., and Stose, G. W., Geology and mineral Codorus Creek and a large tributary, Mill C 'eek. East resources of the New Holland quadrangle, Pa.: Penn of this basin in the eastern part of the York quadrangle sylvania Geol. Survey, 4th ser., Topog. and Geol. Atlas, the upland is drained eastward chiefly by Muddy Creek. Many lateral branches of these major streams run north 2 Walcott, C. D., The Cambrian rocks of Pennsylvania : TJ. S. Geol. Survey Bull. 134, pp. 9-19, 1896. east and southwest and give rise to a poorly developed "Mem., pp. 17-18. trellised drainage pattern, SURFACE FEATURES
The highest part of the southeastern upland forms an slightly lower ridges. From Huntrick Hill southwest irregular ridge which crosses the central part of the to West Manheim, the dissected upland from 900 to York quadrangle and passes through Eed Lion, Einely, 1,000 feet in altitude reaches 1,100 feet near Wentz Shrewsbury, and south of New Freedom. In the vicin in Carroll County, Md. These hills are capped by ity of Red Lion, the summit of the ridge is over 900 quartzites which control their direction and height. feet above sea level and attains 1,000 feet at a point east The southeastern upland as a whole slopes north of Yoe. The divide is mostly below 900 feet from Red westward to the Hanover-York Valley where it termi Lion to Winterstown; but southward as far as Shrews nates abruptly at altitudes between 700 and 900 feet bury it is broader and more than 1,000 feet in altitude. along a line that trends northeastward parallel to tho At Mount Olivet Church one sharp hill attains an alti rock structures. tude of 1,080 feet. South of Rinely the trend of the The Hanover-York Valley crosses the northwest central divide changes from southerly to westerly and third of the area, extending from its northeast border
AND RIDGES
ARRISBURG
P Ej^N_S Yl VAN IA _ _ MARYLAND
FIGURE 2.—Sketch map showing physiographic divisions in southern Pennsylvania and adjacent part of Maryland. southwesterly, and the westward-trending part sepa southwestward through York and Hanover. The val rates the headwaters of Codorus Creek, which flows ley is in limestone, and northeast of York is about 2 northward, from those of Deer Creek and Gunpowder miles wide, and its floor is about 420 feet in altitude. Falls and its tributaries, which flow southeastward. A tributary of Kreutz Creek has cut a secondary valley The Harrisburg division of the Pennsylvania Railroad in the floor near Hellam Station and Codorus Creek crosses the divide at Summit. Grove through a low gap crosses the valley at York. To the southwest and as at an altitude of 840 feet. far as Nashville at the northeast end of the Pigeon In the York quadrangle the northward-trending part Hills, the valley increases in width to about 4 miles. of this central divide crosses the structures of the crys In this wider part many low hills of shale rise above the talline schists; and, except locally, as north of Red Lion valley to altitudes of more than 500 feet. This part of where the 1,000-foot hill is developed on quartzite, the the valley merges northwestward with the Triassic up location of the divide is not the result of greater hard land of the northwestern part, of the Hanover quad ness of the underlying rocks. West of the valley of rangle. South Branch of Codorous Creek, a series of parallel Between the Pigeon Hills and the southeastern up ridges trending southwestward has a general elevation land southwest of Nashville the valley is constrictei to of 1,000 to 1,100 feet. Rocky Riclge, the highest point a width of 2 miles, and expands again to a width of in the southeastern upland, is underlain by the Wissa- 4 miles in the vicinity of Hanover where it is nearly hickon formation and parallels Dug Hill and other flat and has an altitude of about 600 feet. The valley GEOLOGY OF THE HANOVER-YORK DISTRICT, PA. floor, therefore, rises southwestward, away from the West Branch drain the eastern end of the York Valley. Susquehanna River. Deer Creek heads in the southern part of the York The lowest point in the Hanover-York district is not quadrangle, flows southeast across Maryland, and in the Hanover-York Valley but in a valley also with a empties into the Susquehanna River. The headwaters limestone floor in the southern upland. There Cana- of Gunpowder Falls and Beetree Run rise on the south dochly Creek has cut down to an altitude of 240 feet and side of the Shrewsbury divide and drain southward at this point is only a quarter of a mile from its mouth into the Gunpowder Falls, a part of the GH-sapeake at the Susquehanna River. The highest point in the dis drainage system. trict is in the Pigeon Hills, which rise as much as 600 feet Headwaters of Conewago Creek drain the southwest above the limestone valley at Hanover, have a general corner of the district. North of the Pigeon Hills the altitude between 1,000 and 1,100 feet, and attain a creek re-enters the northwestern part of the area and maximum of 1,240 feet. The Pigeon Hills die out at flows across it for 8 miles. Little Conewago C~eek rises Nashville, where the hard Cambrian quartzites that on the north slope of the Pigeon Hills, flows northeast form them plunge under softer, overlying rocks. A ward across the northern part of the Hanover quad similar line of hills northeast of York is the south rangle, and joins Conewago Creek in the Middletown west end of the Hellam Hills, most of which are in the quadrangle not far from the border of the district. Middletown quadrangle north of the York quadrangle. A low upland or dissected low plateau, which is a AREAL GEOLOGY part of the Gettysburg Plain, lies northwest of the GENERAL FEATURES Pigeon Hills and that part of the Hanover-York Valley between York and Nashville. It coincides with the The rocks of the Hanover-York district (pi. 1) com area of outcrop of the Triassic rocks in the northwest prise pre-Cambrian crystalline rocks of both igneous ern part of the Hanover quadrangle. Most of the low and sedimentary origin, lower Paleozoic sedimentary ridges on this upland trend northeastward; but Cone- rocks, and Triassic rocks, both sedimentary and intru wago and Little Conewago Creeks, which cross the low sive. Quaternary alluvium and gravel are alro present plateau, have not developed a systematic dissection be along most of the larger streams. cause the Triassic beds are not hard enough to control The Triassic rocks form the surface of the north the erosion. The average height of this upland is 500 western part of the Hanover quadrangle. ThQ-y consist feet above sea level, but it increases to 600 feet in the of red or gray conglomerate, sandstone, and shale in extreme northwest corner. truded by diabase dikes and the Gettysburg diabase sill. Triassic dikes penetrate also the older rocks to the south DRAINAGE east. The Triassic sedimentary rocks overlie uncon- The Hanover-York district is drained principally by formably the Cambrian and pre-Cambrian rocks ex Codorus, Muddy, Fishing, and Conewago Creeks, which posed southeast of them. flow into the Susquehanna River. In the southern part The Paleozoic and pre-Cambrian rocks belong to two are the headwaters of a few streams that flow south into belts. The northwestern belt is northwest of the Martic Chesapeake Bay. Codorus Creek with its East, South, overthrust and contains folded pre-Cambrian volcanic and West Branches drains most of the central part rocks, Lower Cambrian siliceous rocks, and lov^er Paleo of the area south of the Pigeon Hill divide and west zoic limestones. The pre-Cambrian rocks are exposed in of a main divide, which extends southward irregularly two anticlinal areas—the Pigeon Hills #nticlinorimn, across the central part of the York quadrangle. South north of Hanover, and the Mount Zion anticline, which and West Branches rise near Summit and West Man- forms the southwest end of the Hellam aiiticlinorium. heim, and East Branch rises south of Shrewsbury just These pre-Cambrian rocks are overlain unconformably north of the Maryland State line. These three branches by Lower Cambrian conglomerate, quartzite, slate, and join a few miles south of York to form Codorus Creek, phyllite, followed by Lower Cambrian limestones and which flows north through the city and empties into the Conestoga limestone, in which the Hanover-York the Susquehanna River 5 miles north of the district. Valley was formed. On the south side of the York Mill Creek, another large tributary, joins the main Valley, the Antietam quartzite of the Cambrian system stream north of York. comes to the surface on the northwest limb of the Fishing Creek and North and South Branch of Strickler anticline, which is largely covered in this area Muddy Creek head in the southeastern upland east of by the Stoner overthrust block. Lower Cambrian the main divide and drain eastward and southeastward arenaceous rocks form most of the Stoner block and directly into the Susquehanna River. The upper are exposed in the Mount Pisgah, Kraft Mill, and Holts reaches of Kreutz, Cabin, and Canadochly Creeks, anticlines. These arenaceous rocks are of a facies some smaller tributaries to the Susquehanna, drain the north what different from the Lower Cambrian rod's exposed eastern part of the district. Kreutz Creek and its north of York Valley. They are overlain by lower PRE-CAMBRIAN ROCKS OP THE PIGEON HILLS
Paleozoic limestones in the East Prospect and Jefferson Similar volcanic slates and porphyritic aporhyolite are synclines adjacent to the Martic overthrust. exposed in the Hellam Hills.6 These anticlines and synclines are structurally part The floor upon which these lavas were poured out of the Honeybrook uplift to the northeast and of the is not exposed in the Pigeon Hills and Hellam Hills nor Catoctin Mountain-Blue Ridge anticlinorium to the in the Catoctin Mountain-Blue Ridge anticlinorium southwest, from which they are separated for a distance farther southwest in Pennsylvania and northern Mary of 20 miles by Tiiassic sedimentary rocks. (See fig. 26.) land, where volcanic rocks likewise form the pre-Cam In southern Pennsylvania the Triassic belt trends across brian core of the uplift as far south as Middletown, the strike of the Paleozoic structures, and separates the Md. In the Catoctin Mountain-Blue Ridge anticli Pigeon Hills anticline from the anticlines of pre-Cam- norium south from Middletown and across Potomac briaii and Lower Cambrian rocks in South Mountain in River in Virginia, volcanic rocks border the uplift the Fairfield and Gettysburg quadrangles.* This belt of and the floor upon which the volcanic rocks were poured Triassic rocks also separates the Hanover Valley from out is exposed in the center of the anticlinorium. This the Frederick Valley of Maryland in which Antietam floor consists of an injection complex of earlier pre- quartzite and overlying Upper Cambrian and Lower Cainbrian age. The rocks, beginning with the oldest, Ordovician limestones are exposed. are mica schist and gneiss, hornblende diorite, in The southeastern belt consists of rocks of the Martic trusive granites, porphyritic augen gneiss, injection overthrust block, which occupies the southeastern part gneiss, and migmatite which formed by the injection of of the district. The northwest boundary of the Martic granitic intrusives in the older mica schist and hern- overthrust block extends southwestward from a point blende diorite. This group of rocks is much older than 1 mile south of East Prospect to the southwest corner the pre-Cambrian volcanic rocks which once covered of the district. The rocks of the Martic overthrust it in the center of the uplift as well as on the limbp of block are closely folded crystalline schists of probable the anticlines where they are now preserved. The age pre-Cambrian age. At the northwest they comprise the relation of the two pre-Cambrian series and their ex Marburg schist and associated quartzites, and farther tent hi Maryland and Virginia have been briefly de southeast they are the albite-chlorite schist f acies of the scribed by the authors 8 of this report. The evidence that Wissahickon formation, the Wakefield marble, meta- the volcanic flows are younger than the injection com basalt flows, and metamorphosed tuffs and phyllites. plex is briefly as follows: (1) So far as is known by the writers, the granitic intrusive rocks of the Catoctin The pre-Triassic rocks of the northwestern belt, Mountain-Blue Ridge anticlinorium do not penetrate the including pre-Cambrian rocks of the Pigeon Hills and volcanic series. (2) The metadiabase dikes, which the overlying Paleozoic sedimentary rocks, are described writers regard as syngenetic with the metabasalt, cross first, the rocks of the Martic overthrust block next, and cut the intrusive rocks and gneisses, bevel their stric the Triassic rocks last. tures, and show chilled margins and sharp contacts with the older rocks. (3) The granitic intrusions were con PRE-CAMBRIAN ROCKS OF THE PIGEON HILLS temporaneous with the folding, and these processes to GENERAL. DESCRIPTION gether with the resulting thermal inetarnorphism pro duced the effects now seen in rocks of the injection com The pre-Cambrian rocks of the Pigeon Hills are plex; whereas the overlying volcanic flows, which are metamorphosed volcanic rocks and are exposed in two little metamorphosed except where they were involved anticlines southeast of Abbottstown. The southern in Paleozoic orogeny, were not affected by the granitic most exposure, which is in the Gnatstown anticline, is intrusion and accompanying metiamorphism and ob very small. Together with the overlying basal Cam viously were extruded at some later time. (4) At many brian beds, it is thrust northward along the Gnats- places in Virginia arkose, conglomerate, and voles nic town overthrust onto Lower Cambrian rocks of the High breccia containing pebbles and angular blocks of granite Rock anticline. The northern exposure extends 4 miles and diorite lie at the base of the volcanic series and along the strike in the High Rock anticline and has a overlie the injection complex. maximum width of 1% miles. Basal Triassic sedimen tary rocks overlap the north side of these older rocks METABASALT for 3 miles. Most of the volcanic rocks are green, mas Metabasalt is a massive green rock, often called green sive, amygdaloidal metabasalt. Blue slates containing stone, composed of feldspar, epidote, hornblende, chlo- flattened green amygdules occur in some places in the metabasalt. The slates may be metamorphosed ande- B Jonas, A. I., and Stose, G. W.: Geology and Mineral Resources of the Middletown quadrangle, Pa., U. S. Geol. Survey Bull. 840, pp. f-12, site or rhyolite tuff but were not mapped separately. 1933. 6 Jonas, Anna I., and Stose, G. W., Age relations of the pre-Carat rian * Stose, G. W., U. S. Geol. Survey Geol. Atlas, Fairfield-Gettysburg rocks in the Catoctin Mountain-Blue Ridge and Mount Rogers anti- folio (No. 225), p. 4, 1929. clinoria in Virginia: Am. Jour. Sci., 5th ser., vol. 237, pp. 575-593. 1989. 6 GEOLOGY OF THE HANOVER-YORK DISTRICT, PA. rite, quartz, and magnetite. It is spotted with light- overlain unconformably by basal Lower Cambrian sedi green or white amygdules containing either epidote or mentary rocks. In the Pigeon Hills the metabasalt and quartz, or both minerals. The amygdules may weather blue tuffaceous slate appear to be interbedded, but out in relief and stand out as knots on the surface or may crops are not sufficiently good to prove this relation dissolve leaving a pitted or porous rock. The rock has ship. It is known that in the Catoctin Mountain and been replaced in part by epidote and quartz and is cut by South Mountain areas the rhyolite flows associated veins of these minerals. with tuffaceous slate are older than the basaltic lavas.9 Thin sections show that the massive greenstone has a groundmass of albite, epidote, quartz, and magnetite, PALEOZOIC SEDIMENTARY BOCKS NORTH OF THE and contain phenocrysts of feldspar and the green horn MARTIC OVERTHRTJST blende, uralite, some of which show a core of original The sedimentary rocks of Paleozoic age cross the augite. The amygdules contain hornblende, epidote, cal- area in a belt about eight miles wide between tH Triassic cite, quartz, chlorite, and albite. The albite feldspar of rocks on the northwest and the Martic overthmst on the the groundmass is corroded by secondary hornblende southeast. They comprise Lower Cambrian conglom and chlorite and is itself secondary to more calcic feld erates, quartzites, and phyllites in the Pigeon Hills and spar, some of whose lime went to form the epidote. Mount Zion Hill; limestones, dolomites, and slates of No analyses of the metabasalt of the Pigeon Hills are Lower Cambrian age and argillaceous crystalline lime available but the following analysis is of rock from stone and limestone conglomerates of Ordovician (?) the pre-Cambrian of South Mountain, Adams County, age in the Hanover-York Valley; and Lower Cambrian Pa., an area that was probably continuous with the slates with thinner quartzite beds and phyllites in the Pigeon Hills in pre-Cambrian time. low hills south of the valley. The names, thicknesses, and summary description of the rocks are given in the Analysis of metabasalt from Bechtel copper s7iaft, Soiit7i Mountain 7 accompanying columnar section (fig. 3).
SiO2______41. 280 CAMBRIAN SYSTEM A12O3______18. 480 In ascending order, the rocks of the Cambrian system Fe2O3______9. 440 in this area are the Chickies quartzite with the basal FeO______1 ______8. 200 CaO______7. 040 Hellam conglomerate member, Harpers phyllite, Antie- MgO ______7. 486 tam quartzite, Vintage dolomite, Kinzers formation, NaaO______3. 523 and Ledger dolomite, all of Lower Cambian age. KaO______2. 208 Ign——______2. 740 CHICKIES QUARTZITE NORTH OF THE HANOVER-YORK VALLEY, NAME AND DISTRIBUTION 100.397 VOIX3ANIC SLATE The Chickies quartzite is the oldest of the Lower Cambrian formations exposed in this area. It uncon Blue spotted slate is associated with the metabasalt formably overlies volcanic rocks of pre-Cambrian age. in the Pigeon Hills. The bluish-gray sparkling, sericitic The name Chickies quartzite was applied by Lesley slate contains some flattened amygdules. In places it is and Frazer in 1878 to the quartzites that make Chickies banded with green chlorite. Under the microscope Rock, a cliff on the east side of Susquehar na River, the bulk of the rock is seen to be sericite and ilmenite 1% miles north of Columbia. In York County the or iron oxide dust. The original rock was probably an rocks to which this name is applied are a direct con andesite or rhyolite tuff. Slate having similar con tinuation of the quartzite at Chickies Rock across the stituents and associations is widespread in Carroll and river, but include a thick basal conglomerate member, Frederick Counties, Md., and analyses 8 show that these named Hellam, not exposed east of the river. The slates are low in silica (45.80 percent) for a rhyolite, and Hellam conglomerate member takes its name- from the low in lime (1.15 to 1.77 percent) for an andesite. The Hellam Hills, in York County, where the conglomerate iron oxide content is high (11.73 to 26.91 percent). Al is best developed. though TiO2 is not given in the analyses, it is usually The Chickies quartzite forms the higher pr,rts of the present in these volcanic slates. Pigeon Hills north of Hanover and of the Hellam Hills AGE OF THE VOLCANIC HOCKS northeast of York. In the area south of the Hanover- The volcanic rocks of the Pigeon Hills in the Han York Valley, its representative has a different litho- over quadrangle are pre-Cambrian because they are D Keith, Arthur, Geology of the Catoctin belt; U. S. Geol. Survey 14th Aim. Rept., pt. 2, pp. 309-311, 1894. Bascom, Florence, The ancient 7 Henderson, C. H., The copper deposits of the South Mountain, Pa.: volcanic rocks of South Mountain, Pa.; U. S. Geol. Survey Bull. 136, Amer. Inst. Min. Eng. Trans., vol. 12, p. 82,1884. p. 30, 1896. Stose, G. W., Mineral resources of Adams County, Pa.; 8 Mathews, E. B., and Grasty, J. S., Report on the limestones of Pennsylvania Topo. and Geol. Survey Bull. C-l, p. 9, 192E ; U. S. Geol. Maryland : Maryland Geol. Survey, vol. 8, pp. 370, 378,1009. Survey Geol. Atlas, Fairfleld-Gettysburg folio (No. 225), p. 4, 1929. PALEOZOIC SEDIMENTARY ROCKS NORTH O'F THE MARTIC OVElRTH'RTJST
Formation Thickness Age (feet) Description
~^
wage conglomerate mem "Row zite in lower part of formation, Conewago conglomerate ber. member. t^ilttr4:™™
"Sno New Oxford formation with rTTT.-.-TTTTTTTTTTr-.-.TTTT^TTr Red shale and sandstone with interbedded gray to yellow e conglomerate at and near ,^ arkosic Sandstones; quartzose conglomerate locally at base. base.
T^-T^TTrT-.imn^
Tic -Unconformity——— ———— -L, ——— !_, —— L-,—— !_,—— 1— —— 300-1, 000 Thin-bedded blue limestone with many argillaceous part Conestoga limestone. Oc ings; thick sandy limestone conglomerates in lower part. H-20-3 In part may be of Cambrian age. / / / / / / •€• I i °nn i . J<, '<','< />.±r^ dark-red soil.
Kinzers formation. •T-k 16(MOO Dark shaKbelow; thick marble and limeetone conglomerate above. "w ^/ i L / / / 'r / / / 500-800 a Antietam quartzite. -Ga y^A<:.-.r«"v.--.^--'-i-VS>;w 100-200 White ferruginous granular quartzite. u Harpers phyllite. 800-1,000 Gray-green phyllite and banded slate, with thin quartz €hp ites. Chickies quartzite with Hel -Cc -•.•.;.•.•.•.;•:'•.••';•.•..•;„•,.'.•.••:.•••.••'-'•. lam conglomerate mem 400-900 Massive quartzite, with basal conglomeratic quartzite and ber. f,h 'ytfj&^^^&ffz, slate; 500 feet thick in Hellam Hills. A Metabasalt. mb ?&tiSA Altered basalt flows and tufls. Vert ic al scale 1,0 O O O 5,000 Feet
FIOURE 3.—Columnar section of sedimentary rocks north of the Martic overthrust in the Hanover-York district. logic character and, therefore, is called the Chickies reaches La Bott, and that in the southern fold extends slate and is described separately. to a point half a mile west of Nashville. At the south The Chickies quartzite with its basal Hellam con west, the Chickies in both folds is greatly narrowed and glomerate member surrounds the core of pre-Cambrian broken by faults. The Hellam conglomeratic mem metabasalt in the Pigeon Hills except where the Tri- ber predominates over the quartzite in the Pigeon Hills, assic beds overlap the northern edge of the metabasalt. where hard conglomeratic beds make all the high peaks The formation is here folded into two anticlines which and ridges. Stratigraphically lower beds of softer con extend for about seven miles along the strike. The glomerate and arkosic quartzite with black slate at the quartzites in the southern, or Gnatstown, anticline make base are exposed in the cores of the anticlines and form the southern part of the Pigeon Hills. The quartzites the inner slopes of the ridges. The white Scolithus- in the northern, or High Rock, anticline make High bearing quartzite of the upper part of the Chickies Rock and other high peaks, one of which has an alti formation makes the outer slopes. The lower division tude of 1,240 feet and is the highest point in the district. of the Hellam conglomerate member is separately The two anticlines of Chickies quartzite plunge north mapped in the Pigeon Hills. eastward. The quartzite in the northern fold nearly Northeast of York, the Chickies quartzite on Mount 8 GEOLOGY OF THE HANOVE Zion Hill, which is the southwest end of the Hellam Chickies quartzite—Continued. • Feet Hills, extends only a short distance into the York quad Thin-bedded white quartzite and coarse, granular blue rangle. This part of the hill is composed largely of quartzite containing grains of blue and dark glassy quartz and feldspar and small pebbles_——___— 20rt the Hellam conglomerate member, only a small area at White thin-bedded quartzite interbedded witl thin the western end near Condorus Creek being of the dark slate______40± quartzite. Except two small exposures of quartzite, the Slate and thin beds of quartzite banded with slate_ 50± Chickies is cut out by faulting on the south flank of the Thin- and thick-bedded white sericitic quartzite con Mount Zion anticline. taining Scolithus tubes; weathers to crumbly sand- rock and white sericitic clay______—_— 15± CHABACTER AND THICKNESS Thick-bedded vitreous white quartzite—__—_—_ 20± Thin-bedded vitreous white quartzite; beds generally The Chickies quartzite at the type locality, Chickies less than 5 feet thick; contains many Scolithus Rock on Susquehanna River north of Columbia, is a tubes______1GO± massive well-bedded white vitreous quartzite. It con Very massive vitreous white quartzite; beds 2^ feet thick (Base of Chickieg quartzite not exposed)_— 70± tains the worm boring, called Scolithus, a small round silicified tube lying perpendicular to the bedding. The 335± upper beds are coarser grained and arkosic and contain The section is confused by faulting and repetition of some black slate layers. The Hellam conglomerate beds, as shown by sketch sections in the Middletown member forms the base of the formation in the Hellam report.10 Hills west of the river but is not exposed at Chickies A section of the basal Hellam conglomerate member Rock. This member consists of quartzose conglomerate, where it is thickest follows: arkosic quartzite, and interbedded dark slate. In the Hellam Hills, north of the York quadrangle, the Hellam Composite section of Hellam conglomerate member along the member contains thick beds of coarse conglomerate, river bluff west of Accomao some layers of which are made up of rounded cobbles. Feet (See pi. 2, A and B.) The conglomerates continue into Chickies quartzite: Thin-bedded ScoZitfftM^-bearing quartzite __—_————————————————————————— 200 ± Mount Zion Hill, in the York quadrangle, but the coarse cobble bed does not occur there. Hellam conglomerate member: In the Pigeon Hills the composition of the Chickies Black slate______—_———— 20± Conglomerate and thick-bedded pebbly qurrtzite quartzite is similar to that in the Hellam Hills. The with sericitic quartzose matrix———————— 40 ± conglomerate beds are thicker but are not so coarse Concealed—__———______———————————— 100+ and have more interbedded quartzite. The slate at the Purple-banded coarse-grained arkosic quartzite base is mapped separately. containing pebble and conglomerate bed^; up A continuous unbroken section of the formation is not per part covered______—_——— 200 ± Coarse cobble bed 5 feet thick, containing rounded present in the area, but a generalized section from the 3-inch pebbles chiefly of white quartz, and finer Hellam Hills in the Middletown quadrangle follows: pebbly purple arkosic quartzite-————————— 40± Crumbly sericitic quartzite containing glassy Generalized, section of ChicMes quartzite north of the York quartz grains and scattered small pebbles of Valley quartz______100 ± Feet Massive to thin-bedded hard white quartzite, contain 500+ ing numerous Scolithus tubes in lower and middle part and some dark slate and coarser granular Pre-Cambrian: quartzite in upper part—_———__—______300-400 Aporhyolite, cut by shear zone of pink aporhyolite br'eccia Hellam conglomerate member, composed of coarse- containing quartz, hematite, and epidote. and fine-grained sericitic quartz conglomerate in Metabasalt terbedded with white sericitic feldspathic quartz The coarse conglomerate bed is 5 feet thick and is ite, thin layers of green and purple banded quartz composed of well-rounded cobbles 3 to 6 inches in diam ite, and blue and green slate______250-500± eter in a fine-grained quartz and sericite matrix which 550-900± firmly cements the pebbles. The cobbles are mostly milky-white quartz and also include some red and black The following detailed section of the upper part of jasper and quartzite containing black hornblende the formation is in the vicinity of Chickies Rock: needles. Some of the finer conglomerate beds are pur Composite section of tipper part of Chickies quartzite in vicinity ple and green, having a dark-green quartz a nd sericite of ChicMes Rock matrix which contains small pebbles of blue, pink, and Feet Harpers phyllite: Grayish-green phyilite and slate. clear glassy quartz, coarse grains of pink and white Chickies quartzite: 10 Stose, G. W., and Jonas, Anna I., Geology and mineral resources of Thin-bedded quartzite and interbedded thin dark the Middletown quadrangle, Pa.: U. S. Geol. Surv. Bull. 840, figs. 2 slate ______.______20± and 3, p. 13, 1933. GEOLOGICAL, SURVEY PROFESSIONAL PAPER 204 PLATE 2 A. COBBLE BED IN HELLAM CONGLOMERATE MEMBER OF CHICKIES QLARTZITE AT B. FLAT-LYING COARSE PEBBLE BEDS IN HELLAM CONGLOMERATE MEMBER OF CHICKIES HIGHMOUNT, MIDDLETOWN QUADRANGLE. QUARTZTTE, C. CLOSELY FOLDED CHICKIES SLATE, EAST BANK OF SUSQUEHANNA RIVER ABOUT iy2 D. EROSION REMNANT OF QUARTZITE BEDS IN CHICKIES SLATE FORMING ROCK PIN MILES SOUTH OF COLUMBIA. NACLE IN FLOODPLAIN OF CODORUS CREEK NEAR BRILLHART. Sericitic quartzose beds (light) banded by dark slate and cut by vertical cleavage. Preserves crest of an anticline. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC O'VElRTHRTJST 9 feldspar, and some angular fragments of green quartz- Chickies quartzite—Continued. ite. At the base in some sections are thin beds of Hellam conglomerate member—Continued. Feet Arkosic quartzite containing scattered pebbles; shiny green or blue slate, some interbedded fine quartz- at top a hard pebbly bed 10 feet thick of round ose layers, finely banded magnetite-bearing quartzite white quartz pebbles 1 inch in diameter; near with glassy quartz grains and green and black slaty base a hard 5-foot bed ofjcoarse rounded quartz bands 2 inches thick. cobbles, 3 to 6 inches in diameter_____—_— 35 ± Thick granular purple, banded arkosic quartzite The upper part of the Chickies quartzite is well ex containing scattered pebbles____——————— 60± posed in quarries and in the banks of Codorus Creek "* Conglomerate of unassorted, quartz pebbles scat at the west end of Mount Zion Hill in the York quad tered through greenish sericitic, arkosic matrix- 80± rangle (fig. 4) where the following section occurs: Black slate______.______10 ± 505± Section of tipper part of tlie Chickies quartzite at west end of Pre-Cambrian: Metabasalt and spotted green and blue Mount Zion-Hill, along Codorus Greek volcanic slate. Feet Harpers phyllite: Sandy phyllite with quartzose layers; No section was measured in the Pigeon Hills because chiefly west of creek. the formation is so broken by faulting that none is com Chickies quartzite: plete. The sequence of beds is best shown in the sharn Thin-bedded crumbly quartzite, quarried for sand in ravine on the south side of the mountain, 2 miles north Elmer B. King & Bro. quarry; many Soolithus of New Baltimore, where the water supply for Hanover tubes in the quartzite; some beds have purplish tint is obtained. The following sequence of beds with ap and all weather rusty. Upper bed, 3 feet thick, of proximate thicknesses represents the Chickies quartzite hard quartzite having rough bedding surfaces and laminated by cross bedding; weathers light buff_ 120± in the Pigeon Hills: Thick-bedded vitreous quartzite; Scolithus in upper Composite section of ChicJcies quartzite and Hellam menibir beds______80± with estimated thicknesses in the Pigeon Hills Hellaru conglomerate member: Black and white, banded slate and thin beds of Chickies quartzite: - Fee*, gray to green and dark, banded argillaceous White vitreous quartzite, Scolithus-beaving_———— 200± quartzite; 3-foot bed of granular quartzite and Hellam conglomerate member: some fine quartz conglomerate near the base_ 200 ± Massive-bedded conglomerate; some beds 20 feet thick makes high ridges and peaks______Thick white, rusty-weathering, feldspathic quartz- Thin-bedded crumbly conglomerate______300± ite; coarse-grained, rust-specked quartzite to Coarse conglomerate containing dark slate frag fine conglomerate containing small dark shale ments-_——-______pebbles. Base not exposed______20± Dark slate______-______20± 420 ± 520 ± Pre-Carnbrian rocks: The black and white slate is exposed in the river bluff Spotted volcanic slate. east of the bridge of the Pennsylvania Railroad across Arnygdaloidal inetabasalt Codorus Creek, on the upland to the southeast, and on the road crossing the hill to Pleasureville. It is also AGE AND COBREL?TION exposed in the lowland northeast of Pleasureville, in the The Chickies quartzite north of Hanover-York Valley Middletown quadrangle. (See fig. 4.) unconformably overlies metabasalt and aporhyolite of The Hellam conglomerate member is exposed on pre-Cambrian age and contains pebbles of blue ard Mount Zion Hill in the northern part of the York quad white quartz and slate derived from those rocks. TH rangle and adjacent part of the Middletown quadrangle, finer arkosic layers were derived in part from disinte but the sequence of beds and their thickness are diffi grated "greenstone" and aporhyolite. Scolithus tubes cult to determine. A composite section with approxi are the only fossils in the Chickies quartzite, but tl °. mate thicknesses is as follows : formation is conformably overlain by rocks that contain Lower Cambrian fossils and is therefore classed as Composite section of Hellam conglomerate on Mount Zion Hill Lower Cambrian. The Hellam conglomerate, the bas^l Chickies quartzite: member of the formation, was named from the Hellam Hard vitreous Scolithus-bearing quartzite. Hills in the Middletown quadrangle, where it is be?t Hellarn conglomerate member: Feet developed. Black and white, banded slate and thin quartzite CHICKIES SLATE SOUTH OF THE HANOVER-YOBK VALLEY beds______200± Hard, granular feldspathic to vitreous, white DISTRIBUTION quartzite, current-bedded in part______20± Argillaceous and ferruginous, banded arkosic South of the Hanover-York Valley equivalent rod's pebbly quartzite______100± are so different from the typical Chickies quartzite north 462857—14———2 10 GE'OLOGY OF THE HANOVER-YORK DISTRICT, PA. of the valley that they are described under the heading CHARACTER OF BOCKS IN THE MOUNT PISGAH ANTICLINE Chickies slate. Because it overlies the Hellam con 111 the Mount Pisgah anticline the Chickies is com glomerate member and underlies the Harpers phyllite, posed of black slate interbedded with thir quartzite. the slate is identified as the equivalent of the massive Chickies quartzite north of the valley. The Chickies The best exposures are in the gorges of Kreutz and Mill slate occurs in three anticlines south of the valley, but Creeks, where the streams cut directly across the anti cline, and 011 the East Branch of Codorus C^eek north the basal Hellam conglomerate member is exposed only east of York New Salem, where quartzite forms rocky in the northeastern anticline. In these anticlinal areas cliffs. Chickies slate is surrounded by Harpers phyllite, and The general slaty character of the formation is best the formations together form a belt about 3 miles wide shown in a quarry in the bluff on the east bank of the in the Stoner overthrust block southeast of the Hanover- Susquehanna Kiver south of Columbia. Ths rock ex York Valley. posed is chiefly black shiny slate with numerous thin The Chickies slate is exposed along the axis of the platy layers of gray to rust-stained quartzite and layers Mount Pisgah anticline and makes a series of prominent of thicker quartzites in 2- to 3-inch beds containing black Vintage dolomite Harpers phyllite =5 Conglomerate Fault T, Overthrust side D, Downthrow 20y Strike and dip *°7 Cleavage FIGUKE 4.—Geologic map of gorge of Codorus Creek north of York, showing detailed areal distribution and interpreted structure of the quartzose Cambrian rocks at the plunging end of the Mount Zion anticline. Four stratigraphic divisions of the Chickies quartzite are mapped. hills which are about a mile wide and extend from the slate partings. The beds are folded tightly, and the northeastern edge of the district southwestward to York folds are overturned to the north so that all the beds dip New Salem. Along the same anticlinal axis, northeast southward about 80°. The sequence of beds is uncer of Berkheimer School, is a small exposure of the slate. tain, but a thicker-bedded quartzite is believed to mark Chickies slate crops out in the Holtz anticline, 2% miles the center of an anticline, with a zone or zones of thin- southeast of the Mount Pisgah anticline, and extends bedded quartzites in slate on the flanks. Sericitic from a point 2 miles east of Holtz southwestward to the quartzose beds with black slate layers are shown in East Branch of Codorus Creek southwest of Spry. plate 2, G. This fold is double, as indicated by two parallel bands The quartzite beds have been separately napped only of quartzite exposed on the axes. In the Kraft Mill where they make conspicuous outcrops or debris-covered anticline, which lies southwest of the Holtz anticline but ridges. A thick quartzite above the Hellam conglom not along the same axis, Chickies slate extends from erate has been mapped on the north flank of the anti East Branch of Codorus Creek southwestward for 12 cline from Kreutz Creek gorge to the river. Quartzite miles across the West Branch of Codorus Creek at Kraft occurs also along the Stoner overthrust at several locali Mill. ties, such as Leiphart Mill, on the road southwest of PALEOZOIC SEDIMENTARY' ROCKS NORTH OF THE* MARTIC OVERTHRUST 11 Stoner Station, and places to the east in the Middle- anticline is cut through by Codorus Creek, 1 mile nor^h town quadrangle. Quartzite, repeated by folding, is of Brillhart, which has left a remnant of the quartzite well exposed at a point north of Benroy, at the Paper at the axis of the anticline preserved as a rock pinnacle Mill on Mill Creek, on the hills southeast of York, and which rises 20 feet out of the stream flood plain. (S<\e in the gorges of East Branch and West Branch of pi. 2 D.) In the eastern end of this fold the quartzite Codorus Creek. is exposed east of the road above Codorus Creek, iy2 Several zones of quartizite beds have been observed miles southwest of the Violet Hill reservoir. In the in the slate but, because of poor exposures and repeti cliffs below the York Country Club the quartzites are tion by folding, they cannot be traced far on the sur closely folded and an overturned anticline is exposed face. In the northern part of the Mount Pisgah anti (fig. 7) . Close folding of quartzite in the Chickies abo cline the lower beds of the Chickies slate are exposed is exposed south of Lehman, where the cleavage dip^ in the stream gorge south of Violet Hill. The struc 60° SE. ture there is interpreted as an anticline. (See fig. 5.) A complete section of the formation can only be ap The following section shows the character and se proximated because of the close folding, faulting, and quence of the beds : poor exposures. The following composite section is based on scattered, partial sections and is a revision of Partial section of Chickies slate south of Violet Hill the section previously published.11 Black slate, banded with lighter-colored sandy beds. Thin-bedded green quartzite (2-foot beds) in black Generalised, composite section of Chickies slate in Mount banded slate ——— _ — _ —— ______20± anticline Black slate containing some thin, platy quartzite ______) Harpers phyllite : Green muscovite-quartz schist. Black slate banded with yellow earthy, sandy beds and 1 50± Chickies quartzite: Feet. green phyllite —————— ______j Thin-bedded quartzite and black slate —————— _ — 2f ± Thick-bedded greenish quartzite ______30± Black slate and thin, platy green phyllite inclosing a 5-foot bed of hard white coarse, granular quartzite- 6J'± 100± Thin-bedded greenish quartzite (2-foot beds) with The exposure of quartzite and phyllite on the east side black slate partings and interbedded black slate __ 20 ± Black slate ; some beds banded with yellow earthy- of Mill Creek south of Plank Road, which is interpreted weathering, siliceous layers and green phyllite, and as a syncline (fig. 6), shows the following sequence: a few thin, platy quartzite beds —— ______— _ ___ 50± Thick-bedded quartzite ; some beds 12 feet thick ; thin Partial section of Chickies slate on Mill Creek ner-bedded quartzite at top and bottom- — _ _ _ _ _ 60± Harpers phyllite: Green phyllite. Black slate with a few thin quartzite beds——— _ — 100± Chickies slate: . Feet Hellam conglomerate member : Thick beds of conglom Black slate______10± erate, containing pebbles 1% inch in diameter; in Thin-bedded quartzite______15± terbedded sericitic quartzite and thin black slate _ 80± Black shale and thin green phyllite, and a 5-foot bed of white coarse, granular quartzite______— 65±: 350± Thin-bedded rusty weathering granular quartzite with Based not exposed. black slate partings and thin slate beds____'___ 20± Black banded slate______50 ± The gray muscovite quartzite with dark slate bands, Hard thick-bedded coarse vitreous quartzite contain from the upper part of the Chickies slate in the Pisgah ing blue quartz grains (exposed in anticlines)__ 20± anticline, show in thin section that the'constituents are quartz, muscovite, and chlorite, with some zircon and 180± tourmaline. The clastic quartz grains are somewhat The thick quartzite at the base of this section is be granulated. Chlorite and muscovite fibers lie parallel lieved to be the equivalent of the quartzite exposed in the to the cleavage and at an angle to the banded quartzose bluff at the junction of the West and East branches of layers which indicate the bedding. The blue-gray fine Codorus Creek, which there is estimated to be about 60 grained slate layers show only slaty cleavage and r.re feet thick. composed of chlorite, muscovite, quartz, and fine alfrte The exposures east of the York and Windsor Electric grains. The slate contains also muscovite porphyro- Railway, 2 miles south of York, also show anticlinal blasts which are not oriented with the cleavage. structure (fig. 5). Quartzite in a closely folded anti In thin sections the phyllite layers of the Chickies cline is exposed east of the highway (U. S. Ill) ]'ust slate show alternate micaceous and quartzitic bands. south of the outcrop shown in figure 5. Northeast of The platy minerals—muscovite and chlorite—are par York New Salem quartzite occurs in a compound fold. allel to the cleavage. The rock contains also quartz The quartzite in the northern anticline is undercut by and albite. Muscovite and chlorite porphyroblasts con- Codorus Creek and forms the top of a cliff 200 feet high » Stose, G. W., and Jonas, A. I., Geology and mineral resources of the that faces north and is visible for miles. The southern Middletown quadrangle, Pa.: U. S. Geol. Survey Bull. 840, p. 18, If 33. 12 GEOLOGY 01* THE HANGVE'R-YORK DISTRICT, PA. tain zircon inclusions with pleochroic haloes. The phyl- plunges and the conglomerate member passer under the lites are the result of low-rank progressive meta- slate and does not reappear at the surface to the west. morphism. The rock of the Hellam member is a cream to green schistose quartz conglomerate containing blue and milky HELLAM CONGLOMERATE MEMBER quartz grains and pebbles as much as half an inch long The Hellam conglomerate member of the Chickies and jaspery hematite which colors the rock pink to red slate is exposed only northeast of the Kreutz Creek on weathering. Cleavage planes in the conglomerate gorge, in the center of the Mount Pisgah anticline, where are coated with green muscovite. The conglomerate it forms a series of ledges along the narrow ridge which layers are interbedded with sericitic quartzite and thin rises to an altitude of 840 feet at Mount Pisgah. The black slate. NW. FIGURE 5.—Sketch of section, showing interpreted structure of quartzite beds in the Chickies slate along the York & Windsor Electric Railroad, south of Violet Hill, 2 miles south of York. Chickies slate —*» v '^J N \*\ \\\ I \ \V\ ^O"* \\ L \\V-Harpe.rs-'' ', \\ V\\ \rT\ \ ^N *——i£jA phyllite ^ \\^rfC ^ ^\ "^m^^ \^T7.»vtxx,v^^vv J^s^^fv FIGUKE 6.—Sketch of section of Chickies slate and interbedded quartzite on east side of Mill Creek south of Plank Road, showing interpreted structure. York Country Club FIGURE 7.—Sketch of section showing anticlinal structure of quartzite beds in Chickies slate east of Codonis Creek near York Country Club. best exposure of the conglomerate is just west of York- CHARACTER OF ROOKS IN THE KEAFT MILL AND HOLTZ ANTICLINES ana on the east side of Kreutz Creek, where about thirty Only the upper part of the Chickies slate is exposed in feet of beds are exposed. It crops out on the ridges to the Kraft Mill anticline. The harder beds, which form the northeast in two parallel belts which probably rep ridges, are fine-to-medium-grained green quartzite with resent the crests of two folds. Each belt has two ledges of conglomerate, 20 to 40 feet wide, apparently mark muscovite partings and thin interbedded black slate ing the two limbs of a fold. The best exposure is near bands. Certain thick beds of quartzite are full of mag Brenneman School. The pebbles of the conglomerate netite octahedrons, some facets of which are iridescent. are elongated parallel to the cleavage, which dips In some places north of Strickhousers, the magnetite is steeply to the southeast and has obliterated the bedding so abundant that it has been prospected for iron. The in large part. Southwest of Kreutz Creek the anticline rocks are closely folded, and the folds ar?, cut by a PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRTJST 13 prominent transverse cleavage. The beds are repeated by lite and associated formations crop out in a belt about folding, but the depth of the exposures is not sufficient 4 miles wide that extends from the northeast edge of the to give a complete sequence of beds. The general se district southwestward to the Maryland line, beyond the quence seems to be: limits of the Hanover quadrangle. In this belt Harpers phyllite predominates, but there are anticlinal areas of Sequence of beds in Kraft Mill anticline the Chickies slate, already described, as well as infolds Harpers phylite: Gray phylite and quartzose schist with thin of the overlying Antietam quartzite, Vintage dolomite, beds of quartzite containing magnetite. and Conestoga limestone, chiefly in the East Prospect, Chickies slate: Jefferson, and Stormy Hill School synclines. South Black slate and phyllite west of York New Salem the Harpers phyllite was car Thick green ferruginous granular quartzite containing glassy quartz grains and abundant magnetite crystals. ried northwestward on the Stoner overthrust over the Black slate and thin, slabby dark quartzite containing limestones of the Hanover-York Valley. Northeast of coarse quartz grains. Hanover several small klippen of Harpers phyllite now The Chickies slate in the Holtz anticline is similar to lie on the limestone, having been detached by erosion that in the Kraft Mill anticline. Similar magnetitic from the Stoner overthrust block. The southern edge green quartzite beds form a ridge from a point northeast of this belt of Harpers phyllite is bounded by the Martic of Holtz southwestward to East Branch of Codorus overthrust along which the rocks of the Glenarm series Creek. Large blocks of the quartzite are strewn over override the phyllite. the surface of the ridge. The only outcrops are found CHARACTER AND THICKNESS in the valley of Mill Creek. The Harpers phyllite throughout the region is pre HARPERS PHYLLITE vailingly an argillaceous rock. In the area north of the NAME AND DISTRIBUTION Hanover-York Valley, the dark-gray quartzose phyllite is somewhat streaked with light-gray quartzose bands, The Chickies quartzite is overlain by an argillaceous and in places, chiefly in its upper part, has thin quartzite rock called the Harpers phyllite. The name Harpers beds. Bedding in the phyllite is nearly everywhere shale was applied to argillaceous rocks at Harpers obscured by close folding and the development of cleav Ferry, W. Va. It there overlies the Weverton quartzite, age. The parting planes are shiny with fine mica, ^he which is in part equivalent to the Chickies quartzite in best fresh exposures are 2 miles north of York in the the Hanover-York district, and underlies the Antietam gorge of Codorus Creek and north of Glades to the river quartzite. The Harpers shale, therefore, occupies the in the Middletown quadrangle. South of the Hanover- same stratigraphic position in the section at the type York Valley, thick beds of dense green ferruginous locality as does the Harpers phyllite in the Hanover- quartzite and magnetite-bearing gray quartzite in the York district where the argillaceous beds have been phyllite have been mapped northeast of Benroy and metamorphosed to a phyllite. Although the exposures north of the Jefferson syncline from East Branch of of the formation in this district are not continuous with Codorus Creek to a point west of Sinsheim. those at Harpers Ferry, the two areas are part of the Because of close folding and the lack of observable same uplift. bedding, the thickness of the Harpers phyllite can oily The Harpers phyllite crops out on the south slope of be approximated. At John Mummert School on the Mount Zion Hill, where it is overlain by the Antietam southeast slope of the Pigeon Hills, where it lies in quartzite on the flank of the fold, and at the west end, normal position between southeastward-dipping Chick where it overlies the Chickies quartzite on the plunging ies and Antietam quartzites,.the thickness of the Har end of the fold. The phyllite overlies the Chickies pers is estimated to be 1,000 feet. At the west end of quartzite along the southeast slope of the Pigeon Hills. Mount Zion Hill, where the Harpers is well exposed r.nd Near John Mummert School at the northeastern plung clearly defined by outcrops of the enclosing quartzites ing end of the High Rock anticline, the outcrop of the in normal position, the thickness as determined irom formation expands to half a mile in width. On the the width of outcrop and the dip of the adjacent quartz south side of the Gnatstown anticline the extent is ir ites is 800 feet. In the Hellam Hills in the Middletown regular owing to faulting. The phyllite passes under quadrangle the average thickness was estimated to be the overlying Antietam quartzite, as is well shown on 1,000 feet. the plunging end of the fold at Roth Church. The METAMORPHISM phyllite is well exposed at the plunging end of the Gnatstown anticline and in the centers of the minor Under the microscope, the Harpers phyllite of the anticlines farther south. It also forms the core of the Mount Zion and Pigeon Hills areas is seen to be com Po.ttery Hill anticline southwest of West York. posed of albite, muscovite, quartz, and fine blades of South of the Hanover-York Valley, the Harpers phyl biotite, The mineral content and fineness of grain in- 14 GEOLOGY OP THE HANOVER-YORK DISTRICT, PA. dicate that the metamorphism is a mild type of low thrust. Two miles northwest of York and west of the metamorphic rank. South of the Hanover-York Valley, highway (U S 111), a small outlying hill of th°i quartzite on the flanks of the Mount Pisgah, Kraft Mill, and Holtz is the extreme end of this anticline and was H-ought up anticlines, Harpers phyllite is more coarsely crystalline between 2 diverging faults. In the Pigeon Hills the than in-the Pigeon Hills and Hellam Hills. (See pi. Antietam borders the northeastward-plunging end of 3, A and B.) The finely sparkling gray-green phyllite the High Rock anticline around Roth Church and also is composed of muscovite, chlorite, albite, and quartz, borders in part the Harpers phyllite in the Gnatstown and is banded in places with thin quartzose layers. and Menges Mill anticlines to the south. It completely Muscovite and chlorite blades are parallel to the cleav surrounds the Harpers phyllite of the Ambau anticline age, but an incipient growth of chlorite and muscovite and spreads out into a fairly wide anticlinal area north flakes is alined at an angle with the cleavage. The and east of Mount Carmel School. The formation crops phyllite contains tourmaline and ragged porphyroblasts out discontinuously in a narrow strip along a strike fault of ilmenite, some of which have chlorite rims. The rock east of Nashville. It borders the Harpers phyllite on is a paracrystalline phyllite produced by progressive Pottery Hill, a small but conspicuous anticliral hill just metamorphism. The constituents of the rock and espe south of Lincoln Highway (U S 30) and 1 mile west of cially the porphyroblasts are not so coarse as those in West York. the phyllites and schists farther southeast in the Martic South of the Hanover-York Valley, the / ntietam is overthrust block, but the composition is similar to that present in the Stormy Hill School syncline, which en of beds in the Marburg schist lying adjacent to the south closes the long narrow area of Vintage dolomite north east. In the argillaceous layers of the Harpers phyllite, of Porters Siding. South of the Kraft Mill anticline, the only visible structure is a closely spaced cleavage. the quartzite makes relatively wide belts in the Jeffer In the quartzose layers, bedding is observable, espe son syncline where outcrops are well exposed on the cially in the arches of the folds where cleavage direction north side of the syncline and in a subordinate anticline lies across the planes of stratification. Plate 3, #, shows in the midst of the Conestoga limestone. In the south the quartzose-layered variety of Harpers phyllite from westerly extension of the Jefferson syncline, in the area the upper part of the formation. The thin section was southeast of Wildasin Chapel, the Antietam surrounds cut from a specimen that came from the closely folded the Conestoga limestone except where overridden on area near the edge of the Cabin Creek overthrust, 1% the southeast by rocks of the Martic overttrust. The miles west of Margaretta Furnace. A polished specimen largest synclinal area of Antietam south of th°. Hanover- of similar rock from near the same locality is shown in York Valley extends from a point north of Spry to East plate 18, G. Prospect, on the south flank of the Mount Pisgah anti AGE AND CORRELATION cline, and a narrower band continues northeastward to The Harpers phyllite nowhere contains fossils; how the Susquehanna River. The part east of Delroy lies ever, the Antietam quartzite, which conformably over on the north side of the East Prospect syncline, which lies the formation, does contain Lower Cambrian fossils. forms a deep embayment of Conestoga limestone in Consequently, the Harpers phyllite is considered to be of places bordered by remnants of Vintage dolomite. An Lower Cambrian age. area of Antietam quartzite just south of Margaretta Furnace surrounds a syncline of limestone except on the ANTIETAM QUARTZITE south side, where it is cut off by the Martic overthrust. NAME AND Di8TB3BonoN The Antietam quartzite is the uppermost of the Lower CHABACTER AND THICKNESS Cambrian quartzose formations. The name Antietam The Antietam quartzite is a gray quartzite weather was first applied to similar quartzite which is exposed ing to rusty brown on bedding surfaces. The lower on Antietam Creek in South Mountain, Franklin County, part of the formation is finer grainedrand hrs beds that Pa., and which occupies the same stratigraphic position are streaked with dark argillaceous matter, thus grad as the Antietam quartzite of the Hanover-York dis ing into the underlying Harpers phyllite. Hard blocky trict. Although the two areas are not directly con coarse-grained quartzite beds occur near the middle. At tinuous, they are parts of the same structural uplift. The Antietam quartzite forms the outer rim of the the top are granular ferruginous laminated quartzite anticlinal mountains and hills made of Cambrian quartz- beds which weather into porous rusty blocks owing to the ites. Along the southeast flank of Mount Zion Hill, the solution of the calcareous matrix. Molds of fossils quartzite makes a narrow fluted band which curves coated with yellow rust are revealed when the weathered around the southwestward-plunging end of the Mount rock is split on the bedding planes. The darfr-red sandy Zion anticline. At that point the outcrop is sharply soil derived from weathering of these beis contains offset 1 mile by the west branch of the Highmount over- residual iron ore. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OYERTHRTTST 15 The following section of the formation on the south dant. The lithologie character of the Antietam quartz slope of the Hellam Hills, 1 mile west of Wrightsville in ite in the area north of the Hanover-York Valler is the sMiddletown quadrangle is representative of the similar to that in the Strickler anticline. Plate 4, A Antietam in the Mount Zion anticline: represents a thin section of a specimen taken from the Strickler anticline 1 mile north of the edge of the York Section of Antietam quartzite 1 mile west of WrigMsville quadrangle and 2 miles north of Kline School. In the Vintage dolomite: region south of the Mount Pisgah anticline and north Impure sandy dolomite weathering to porous sandstone. of Margaretta Furnace, the biotite porphyroblasts are Antietam qtiartzite: Feet larger. They are plainly visible to the unaided eye, and, Slabby quartzite with rusty partings and fossil im pressions ______40 together with magnetite crystals, speckle the rock. In Coarse, granular porous-weathering fossiliferous thin section (pi. 4, B) the biotite porphyroblasts are quartzite ______I___ 10 irregular in outline and intergrown with chlorite. A Quartzite with argillaceous streaks; weathering similar rock containing abundant porphyroblasts of bjo- granular and white coated_—______150± tite and magnetite (pi. 4,' C) occurs between the Kraft Mill anticline and the Jefferson syncline. On the hill Harpers phyllite: Gr&y phyllite. 200 ± north of St. Pauls Church in the southwest extension South of Columbia, in the Lancaster quadrangle, the of the Jefferson syncline, the Antietam quartzite is finer upper beds of the Antietam quartzite are well exposed grained and its lithologie character resembles that of in the river bluff: the rock in the Pigeon Hills area. The present quartzite was produced by progressive Partial section of Antietam quartsite south of Columbia metamorphism which varied in degree in different pgrts Vintage dolomite: Gray, knotty dolomite; basal beds sili- Feet of the district. The area of maximum intensity lies ceous, and contain a small amount of sphalerite, and in the East Prospect syncline, of the York quad merge downward into pyritiferous calcareous sand stone. rangle, as indicated by the coarse crystallinity of the Antietam quartzite : Antietam and the large size of the contained bioitite Fine-grained laminated gray quartzite and ferrugi flakes. To the southwest and northwest of this syn nous quartzite composed of glassy quartz grains; cline, metamorphic intensity wanes. The zone of contains pyrite and weathers rusty; top layer maximum intensity of metamorphism of the Antietam highly calcareous, pyrite abundant, weathers to rusty siliceous skeleton______10 quartzite in the East Prospect syncline is related prob Well-bedded fine-grained gray quartzite; highly fer ably to that in the belt around Mine Ridge,12 farther ruginous laminated beds contain fossils on bedding east, where the Lower Cambrian Antietam quartzite, planes in lower part______—_—____ 30 the basal part of the Vintage dolomite, the Conestoga Bluish schistose quartzite; no observable bedding; limestone, and the Wissahickon formation contain thickness not determinable. coarse biotite. The variable degree of metamorphism On the flanks of the anticlines of the Pigeon Hills, of the Paleozoic rocks is discussed in the description in the Hanover quadrangle, the Antietam quartzite is of the metamorphism of the rocks of the Martic over- much thinner, and its exposures generally are poor. Its thrust block. thickness here is estimated to be less than 100 feet. On AGE AND OOBBELATION the north side of the Jefferson syncline, along the state road between Seven Valleys and York New Salem, the The upper beds of the Antietam quartzite are locelly^ Antietam is closely folded and has lenticular quartzose fossiliferous. The fossils are internal and external layers parallel to the vertical cleavage. An estimated molds and are generally too poorly preserved to be thickness of 150 feet is probably much too great for this specifically determined. Fragments of olenellid tri- belt of the formation. lobites and the small brachiopod, Obolella, minor, are the most abundant and most diagnostic forms. Wal- METAMOKPHISM cott 13 identified Oaanarellu minor^ Obolella crassa, (?), The Antietam quartzite varies in coarseness of grain Hyolithes commimis^ and Olenellus sp. from these beds size and in rank of metamorphism in different parts of in the vicinity of Emigsville. This list as revised by the area. In the Hellam and Pigeon Hills and Mount Resser,14 is as follows: Oboletta minor', O. crassa (?) Pisgali areas, it is a fine- to medium-grained phyllitic (possibly identical with O. minor), Hyolithes sp., and quartzite, which, under the microscope, is shown to be Olenellus sp. All are Lower Cambrian forms. The composed of quartz, microcline, and albite, with mus- writers collected some of the species listed above ffori a covite forming the schistose partings. It contains small point 3 miles west of Wrightsville. incipient porphyroblasts of biotite and, in places, of 12 Knopf, B. B., and Jonas, A. I., op. citi, (Bull. 799) pp. 129-141. chlorite. The biotite contains inclusions of zircon with 13 Walcott, C. D., The Cambrian rocks of Pennsylvania: U. S. Geol. Surv. Bull. 134, p. 15, 1896. pleochroic haloes. Magnetite porphjToblasts are abun ** Resser, C. B., personal communication, 1&38. 16 GEOLOGY OF THE HANOVER-YORK DISTRICT, PA. VINTAGE DOLOMITE School anticline within the broad outcrop of Kinzers NAME AND DISTRIBUTION formation northeast of Spring Grove. North of Han The Vintage dolomite is the oldest carbonate forma over, the dolomite borders the Antietam quartzite- on tion of the Cambrian system in the Hanover York Val the south side of the Pigeon Hills and curves around ley. The formation was named 15 from its exposures the westward-plunging ends of two small anticlines of along the Pennsylvania Railroad at Vintage station, the quartzite at the edge of the Hanover quadrangle and Lancaster County, Pa. The dolomite grades down in the adjacent Gettysburg quadrangle. A narrow strip ward through calcareous quartzose beds into the An- of Vintage dolomite borders the Antietam quartzite in tietam quartzite and, therefore, generally borders hills the syncline 1 mile northeast of Porters Station. A still of Antietam quartzite throughout the area. smaller area is exposed beneath the Conestoga lime Vintage dolomite in a narrow band a quarter to an stone in the Jefferson syncline north of Seven Valleys. eighth of a mile wide, parallels the hills of Antietam CHARACTER AND THICKNESS quartzite on the north side of the York-Wrightsville The Vintage dolomite may be divided into two parts. Valley. This is the southwest end of a band that lies The lower part is chiefly a blue knotty, "mud lump" between the Antietam quartzite and Kinzers forma tion, which border the south side of the Hellam Hills dolomite, and the upper part, a pure fine-grained lime stone. At the base of the lower division is a white quartz- anticlinorium in the Middletown quadrangle. The oze marble that grades downward into the underlying width of the formation expands to more than a mile Antietam quartzite. Although this basal bed is seen at the westward-plunging end of the fold north of at few places, it is well exposed in a small ravine 1 York. This band passes northward out of the York quadrangle and westward into the Hanover quadrangle mile south of Columbia, in the Lancaster quadrangle, on before it is covered by the Triassic sedimentary rocks. the east side of Susquehanna River. The blue knotty A small area of the dolomite and the underlying An dolomite is well exposed in a quarry south of Wrights- tietam quartzite is brought up in narrow fault blocks ville, on the south bank of Kreutz Creek, wh^re it was 1% miles north of York. quarried for concrete used in the construction of the On the south side of the York-Wrightsville Valley a bridge on the Lincoln Highway (U. S. 30) built across narrow strip of Vintage dolomite between the Antietam the river in 1930. The dolomite exposed there is about quartzite and Kinzers formation extends from Leiphart 100 feet thick, in part well bedded and in part massive Mill southwest to Plank Koad. Vertical beds of knotty with no visible bedding. Other outcrops of the lower Vintage dolomite in a tight syncline in the Antietam knotty dolomite occur in several ravines at the foot of quartzite are exposed in the railroad cut just south of the hills on the south side of the York-Wrightsville Plank Road. At this point these beds are cut off on the Valley and in the valley of Codorus Creek just south of south by the Stoner overthrust. Farther southwest the the point where the creek enters its rocky gorge, 2 miles Vintage is covered by the Stoner overthrust. A narrow north of York. band of the dolomite follows the borders of the folded The higher beds of the formation are mostly pure fine Antietam quartzite in the East Prospect valley in the grained limestone, finely banded or mottled by dark northeast corner of the York quadrangle. Near East wavy layers. These beds are well exposed in many Prospect, the Vintage is overlapped by the Conestoga small abandoned quarries in the vicinity of La Bott. limestone and does not crop out at East Prospect nor These upper pure beds have not been observed in the westward for 2 miles. A small area of Vintage dolomite eastern part of the area where probably they are very is exposed again at the border of the Conestoga lime thin or absent. stone on Cabin Creek, 1 mile west of Margaretta Fur In general the Vintage dolomite is poorly exposed nace, and another is exposed between the Antietam because it is more soluble than the enclosing quartzites quartzite and the Conestoga limestone in the valley 1 and shales and, therefore, forms lowlands, in part cov mile south of Margaretta Furnace. ered with quartzite debris between high hills of An One of the largest areas of the formation is more than tietam quartzite and lower hills of the Kinzers forma 1 mile wide and forms an arc around the Antietam tion. The lower dolomite of the formation weathers to quartzite at the eastward-plunging end of the Pigeon a characteristic granular maroon clay which covers the Hills anticline, east of La Bott. The Vintage dolomite lower slopes1 of the Antietam quartzite hills. borders the Antietam quartzite in several faulted anti Because of poor exposures, the thickness of the forma clinal folds between Nashville and Mt. Carmel School tion is difficult to determine. In the La Bott. area, and underlies the valley southward to the Stoner over- where the formation dips gently away from the plung thrust. It is exposed at two places in the Sprenkle ing end of the Pigeon Hills anticline without duplica tion of beds by minor folding, the thickness, computed 16 Stose, G. W., and Jonas, A. I., Lower Paleozoic section of south eastern Pennsylvania: Wash. Acad. Sci. Jour., vol. 12, no 15 n 362 . from the width of outcrop and the general dip, is 800 1922. feet. In the narrow bands of the formatior west of GEOLOGICAL SUBVEY PBOFESSIONAL PAPEB 204 PLATE 3 '^. HARPERS PHYLLITE, 1 MILE WEST OF JACOBUS. B. QUARTZOSE HARPERS PHYLLITE, SOUTH OF LEHMAiN. Foliation (dark bands) horizontal, cleavage vertical. Muscovite poryphyro- Shows slip cleavage crossing the banding. X 9. blasts (white needles) intersect cleavage at an angle. X 27. C. QUARTZOSE HARPERS PHYLLITE, WEST OF MARGARETTA FURNACE. Shows close folding and vertical cleavage. X 12. GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 4 . ANTIETAM QUARTZITE FROM STRICKLER ANTICLINE. B. ANTIETAM QUARTZITE, EAST OF CANADOCHLY CHURCH. Constituents are quartz and albite (white), muscovite (gray), and biotite Biotite porphyroblasts (b). X 15. (Mack). X 15. C. ANTIETAM QUARTZITE, NORTH OF SEVEN VALLEYS. Schistose phase, with groundmass of muscovite, quartz, and albite. Por- phyroblasls of biotite (b) banded in part with chlorite (c). X 15. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRUST 1.7 Nashville and south westward, the thickness is appar Vintage dolomite—Continued. ently not more than 500 feet. On the south side of the Lower part—Continued. Feet York Valley, southeast of Stoneybrook and eastward Concealed (fragments of sjabby light-blue lime stone with shaly partings). Estimated thick into the Lancaster quadrangle southeast of Columbia, ness ______—_____ 350± the Vintage dolomite is very thin, probably not more Spotted dolomite; weathered surfaces pitted than 200 feet thick; and the upper purer limestone of with flat holes (pebbles?) (quarry east the formation apparently is not present. The thinness of Emigsville) ______25 of the Vintage and Kinzers formations, together with Covered north of Emigsville. (The basal beds are not exposed here but elsewhere are white the absence of some of their members, along the south to pinkish, cream-colored laminated fine east sides of the Wrightsville and Columbia Valleys, grained marble becoming siliceous downward suggests that in this area the sea was shallow during - and merging into the Antietam)___—______200± Vintage and Kinzers time and that the shore was nearby to the south. The most complete exposure of the Vintage dolomite in the region is in the vicinity of Emigsville, just north Antietam quartzite: Rusty quartzite in Pennsylvania of York quadrangle. The following composite section Railroad cut north of Emigsville. was made from numerous disconnected outcrops and ex posures in quarries. The estimated thicknesses in the The Vintage dolomite on the south side of the York- concealed portions may be greatly in error, and the total Columbia Valley is much thinner than near Emigsville, thickness is believed to be not more than 1,000 feet. as is shown in the exposures on the east side of the Sus- quehanna 1 mile south of Columbia: Section of Vintage dolomite near Emigsville Section of Vintage dolomite 1 mile south of Columbia Vintage dolomite: Fee*. Upper part: Feet Kinzers formation: Blue calcareous slate and gray slate. Top of formation concealed by Glade overthrust Vintage dolomite: half a mile south of Emigsville. Blue knotty dolomite______10± Concealed in small stream valley (some beds Concealed in valley, estimated_____—_——___ 40± of white siliceous chalky marble weathering Very massive dolomite-______—_—__—____ 20 to buff tripoli near middle, and some light- Knotty gray dolomite; thin-bedded character brought gray jointed dolomite in upper part). Esti out by weathering; basal layer contains small mated thickness______320± amounts of sphalerite and galena and grades down Pure fine-grained dark-blue and white mottled ward into pyritiferous calcareous quartzite_____ 140± limestone containing some dolomitic bands and lumps (probably same as the Salterella- 210± bearing beds near. La Bott) ______40± Coarsely crystalline white and black brecciated marble and dark-blue glistening dolomite__ 180 ± Antietam quartzite: Calcareous granular quartzite. Light-blue limestone containing coarser dolo , The top of the Vintage dolomite is well exposed in the mite blebs, and blue and white streaked lime stone with dolomite mud-lump structure; Northern Central Railroad cut west of the quarry of weathers knotty and dirty-gray______80 the Universal Gypsum & Lime Co., formerly the Palmer Lime & Cement Co., in West York. These beds contain 620± cystid plates and are of interest because fossils are very scarce in the formation. Lower part: Section of upper part of Vintage dolomite southwest of West York Impure blue and gray mottled sheared dolomite; weathers dirty-gray______40 Kinzers formation: Shale. Dark-gray sparkling knotty dolomite with Vintage dolomite: Feet lighter-gray coarsely crystalline blebs and Gray dolomite; weathers dirty-colored————————— 10± stringers, and thin bands alternately dark Mud-lump dolomite, and impure dark and light dolo and white; mud-pellet layer at top—______15 mite containing coarse crystalline specks_———_ 12 Dark fine-grained dolomite, finely banded and Impure dolomite; weathers to concentric banding.—— 5 showing finely conglomeratic character on Crumbly dolomite; weathers dirty-colored——————— ? weathering——______20 Light-blue limestone; weathered surfaces are white Massive light-gray fine-grained dolomite____ 30 and blue mottled with dark impurities, and bedding (The three units described above are exposed surfaces are pitted and "worm eaten." Contains in a quarry in western part of Emigsville.) cystid plates which weather in relief————————— 7 Light-gray dolomite containing coarser dolo Blue fine-grained dolomite; weathered surface, dirty- mite blebs______35 buff______———-——————— 10 Blue and white laminated marble; fossiliferous blue limestone at top______1___ 90 18 GEOLOGY OP THE HANOVER-YORK DISTRICT. PA. AGE AND OOBRELATION stone member are the sites of Greenmount Cemetery and The few fossils known from the Vintage dolomite of Farquhar Park northwest of York. (S^e figs. 9 include fragments of trilobites, phyllopod shells, and and 10.) On the south side of York-Wrightsville Val cystid plates. ScHterella. conica was found in pure lime ley, from Leiphart Mill to Plank road, the lower shalfl stone beds in the upper part of the formation near La member is a narrow band, the north side of which is Bott and at two places 1 mile east of La Bott. Cystid overlapped by the Conestoga limestone. plates of unidentified genera occur in the limestone in- South of West York on both sides of West Pranch of Codorus Creek, the Kinzers formation occurs in several terbedded with dolomite just above the Antietam quartzite in a cut of the Pennsylvania Railroad south of folds, which are broken by faults. The Universal Gyp sum and Lime Co., formerly Palmer Lime ani Cement West York. Co., has a quarry in the limestone member south of a The fossils that have been identified from the forma hill of basal shale. The Eli Zinn quarry, just south of tion in this and nearby areas are of Lower Cambrian age. York, on the north side of Codorus Creek, is also in this The Vintage dolomite immediately underlies shale and limestone, and the upper sandstone member forms the limestone of the Kinzers formation which contains a top of the quarry and the hill to the north on which large fauna of Lower Cambrian age. Highland Park is located. (See fig. 16.) KINZERS FORMATION The threefold divisions of the Kinzers formation is displayed best near Thomasville, where the dips are low NAME AND DISTRIBUTION on the plunging end of the High Rock anticline of the The Kinzers formation was named from exposures at Pigeon Hills, and consequently the members form wide Kinzers Station on the Pennsylvania Eailroad, Lan bands. The upper sandstone makes the hill southeast caster County, Pa., where its relation to the underlying of Thomasville, and the basal shale makes the cres Vintage dolomite is well shown. In the Hanover-York cent-shaped ridge that curves around the plunging end district the most characteristic features of the formation of the High Rock anticline southwest of Thomasville. are the shale at the base and the impure calcareous and The quarries of the Thomasville Stone and Lime Co. and argillaceous sandstone at the top. These members gen of J. E. Baker & Co., at Thomasville, are in the pure erally make low ridges and in places form prominent limestones of the middle member. hills. A narrow valley formed in the middle, calcareous An irregular belt of hills of the Kinzers formation member generally lies between parallel hills of these enclosing a narrow valley in Vintage dolomite extends harder members. The shale at the base was mapped sep from a point south of West York southwestward to arately throughout the area. In the vicinity of Penn Spring Grove. The anticlinal structure of this belt Grove and north of East Prospect, this shale is the only could be worked out only by mapping separately the part of the formation present. The sandy and earthy shale at the base of the Kinzers formation. The two beds at the top of the formation have been mapped not overlying members are not separated because the upper only where they make conspicuous ridges but also in sandstone beds here are thin. The Kinzers formation places where the ridges were not prominent, because is preserved on the flanks of several minor anticlines, such mapping was essential to solve the structural rela such as those north of Nashville and at Menses Mills, tions. South of the Gnatstown overthrust the upper and north of Iron Ridge it nearly surrounds the anti sandy beds are very thin and were not mapped separ clinal hill of Antietam quartzite. In these areas also ately. the shale at the base was mapped separately. In the The Kinzers formation, with its two lines of ridges limestone cove at Penn Grove, in the areas around and narrow intervening valley, extends along the north York Road, Smith Station, and a point 1 mile north of side of the York-Wrightsville Valley from York north Smith Station, as well as in the eastern part of the dis eastward and crosses the Middletown quadrangle to trict northeast of East Prospect, only shale i* present, Susquehanna River. The shale and sandstone ridges as! the Conestoga limestone apparently overlaps the are very low, but the sandstone ridge is the more con higher beds. spicuous. The town of Hellam, just north of the York CHABACTEB AND THICKNESS quadrangle, is located on the sandstone ridge. The members of the formation are repeated by faulting The Kinzers formation is composed of thrf} distinct. north of Campbell. members. The lower one is a black to gray argilla North and northwest of York the basal shale makes ceous shale. In the vicinity of the Getz quarry in the prominent ridges crossed by the highway (U. S. Ill): Lancaster quadrangle light-gray to light-Wue argil- but, owing to faulting, the ridges are not continuous. lite with hackly fracture contains fine specimens of The shale forms several hills in the York Valley, west trilobites. In the Hanover-York district th^ shale is of York, along the border of the overlapping Triassic closely folded and cleavage is so well developed that the sediments. Prominent isolated hills of the upper sand bedding is obliterated and no fossils have be^n found. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRTJST At many localities the shale contains pyrite cubes or toga limestone and was so shown on the maps in the rusty pits where the cubes have been removed by weath reports. Fossils collected recently from the sandy beis ering. Cleavage planes usually are stained by iron in the York and Hanover quadrangles as well as in the oxide. Southwest of Spring Grove the shale beds of area to the northeast prove the member belongs in the the lower member have been altered into a black, shiny, Kinzers.18 A revised map of the southern part of the finely micaceous phyllite. Middletown quadrangle is shown in figure 24 and on The middle member is predominantly limestone of the geologic map of York County.19 The character of variable composition. Some of it is a pure high-calcium the Kinzers formation is so varied that a large number rock and is extensively quarried by two companies near of detailed sections from quarries and other good ex Thomasville, one in West York, and two west of the posures are presented. Most quarries are in the thick- shale hill that lies 1^ miles west of West York. Sev bedded pure limestone of the middle member; and at eral of the limestone beds have a spotted or mottled ap many of them, the sandy and earthy limestones of the pearance, caused by the enclosure of rounded or lenticu upper division cap the quarry faces. The boundary lar masses of white crystalline limestone in argillaceous between the upper and middle members is not every or earthy layers. These spotted beds are called "leopard where well defined because of the variable occurrence of rock." On weathering, the impure layers stand in re the sandy and earthy beds. lief, and a reticulate earthy network may result. (See In the Lancaster-New Holland area the Kinzers for pi. 5, A.) The "leopard rock" occurs also in the sec mation is 150 to 200 feet thick. The character of the tion at the type locality. The peculiar structure is beds is shown in the following composite section de apparently of organic origin and related to the archae- rived from exposures in the New Holland quadrangle at ocyathid reefs found in some of the purer lime Kinzers, the type locality 13 miles southeast of Lan stones of the formation at the Eli Zinn quarry on the caster, and in the Lancaster quadrangle at Rhorers- east face of Greenmount Cemetery Hill and at the S. town, 3 miles northwest of Lancaster : Forry Laucks quarry. Rocks of the same age near Austinville, Va.,16 contain similar reefs. Composite section of Kinzers formation in, Lancaster and New Holland quadrangles Partial recrystallization in some of the pure beds has produced a conglomeratic appearance. These layers Ledger dolomite: Massive granular gray dolomite. contain rounded residual masses of finely crystalline JKinzers formation: Upper member : dark limestone enclosed in light-gray to white coarser- Impure white marble with siliceous partings; Feet grained recrystallized marble. Other beds are true con weathers to tough tripoli ———————————— 2C± glomerates composed of coarse marble fragments. Pure Sandy dolomite ; weathers to tough hard porous limestone in some beds has been altered in part to coarse fine-grained sandstone. ——— _ ————————— grained dolomite, the replacement starting along frac Concealed ___ —————————————————: — 20 tures and thence spreading irregularly into the mass. 45 ± Middle member: (See fig. 12.) Dark-blue limestone with wavy argillaceous The upper member of the formation is usually an partings and thin layers of gray dolomite__ 30± earthy or fine-grained quartzose limestone containing Dark earthy limestone spotted with white dark argillaceous layers. The beds weather to buff ("leopard rock") ——_———————————— 10 dense, tough tripoli, porous fine-grained sandstone, or Tough sandy fossiliferous blue dolomite; weath ers buff and somewhat ribbed————————— 20 dark dry earthy banded shale. Fossils have been found Dense blue impure limestone with nodules of in the weathered rock at most of its outcrops in the pure limestone ("leopard rock") —————— 6 Hanover-York district. These sandy beds are most con Blue limestone with fine wavy argillaceous spicuously exposed on a prominent hill southeast of laminations _————————————————— 1C Thomasville. 7f± On the north side of the York-Wrightsyille Valley Lower member: also, the upper sandy member makes a distinct low ridge Dark fissile shale————————————————— 35-70 which extends into the adjoining Middletown and Lan Earthy fossilkerous blue dolomite; weathers to caster quadrangles. When the reports 17 on those quad buff or orange-colored tripoli or porous sand rangles were published, this sandy limestone was stone______-_ thought to be the basal part of the overlapping Cones- 42-77 16 Stose, G. W., and Jonas, A. I., A southeastern facies of Lower Cambrian dolomite in Wythe and Carroll Counties, Va. Va. Geol. Sur Vintage dolomite: Massive light-gray dolomite. vey, Bull. 51-A, pp. 10-22, 1938. 17 Stose, G. W., and Jonas, A. I., The geology and mineral resources M Jonas, A. I., and Stose, G. W., Age reclassiflcation of the Frederick of the Middletown quadrangle, Pennsylvania: TJ. S. Geol. Survey Bull. Valley (Maryland) limestones : Geol. Soc. Am. Bull., vol. 47, p. 1671, 1QW, 840, p. 35, 1933. Jonas, A. I., and Stose, G. W., Lancaster quadrangle: 18 Stose, G. W., and Jonas, A. I., Geology and mineral resources of Pennsylvania Geol. Survey, 4th ser., Topog. and Geol. Atlas No. 168, -York County, Pennsylvania: Pennsylvania Geol. Survey, 4th ser., Bull. p. 47, 1930. C-57, pi. 1, 1939. 20 GEOLOGY OF THE BAKOVETl-YORE; DISTRICT, PA. In the reports on the New Holland 20 and Lancaster 21 Kinzers formation—Continued. quadrangles the writers recognized the threefold divi Middle member (north quarry)—Continued. Feet Light-gray dolomite (horse in quarry)——————— 5 sion of the formation but did not separate it into the Very massive-bedded mottled white coarsely crystal- three members. , line marble; some limestone conglomerate ir mid Another nearly complete section is exposed along the dle; thinner bedded at base———————_———— 50+ river bank just north of Wrightsville, where the pure Blue limestone-_-_——_-—————_—————— 10 marble of the middle member has been extensively quar Concealed______80+ ried. In the report on the Middletown quadrangle,22 185 ± these pure beds1 were included in the Ledger dolomite; but now the marble is known to be part of the Kinzers Lower member: formation. (See sketch map and section, fig. 8.) Concealed______——_———— 70+ Dark shale (forms hill)______———__——— 30 Revised composite section of Kinzers formation and overlying limestones north of Wrightsville 100+ Conestoga limestone (south quarry) : Feet Total thickness of Kinzers formation—-___ 420+ Argillaceous limestone conglomerate, banded argil Vintage dolomite: Dark knotty dolomite. laceous blue limestone, and thick granular crystal line limestone______—______The upper part of the formation is well exposed along Black argillaceous limestone and thin shale; ripple the railroad track south of the quarry of the, Thomas- marked______>200± ville Stone and Lime Co. Including the pure beds in the Marble; 2-foot bed____-.___—______quarry and estimating the thickness of the lower shale, Conglomerate composed of dark slabby limestone frag ments and 6-inch angular masses of white marble which is poorly exposed in the ridge to the west, the in black slaty matrix______thickness of the formation here is about 40C feet. Wall rock, concealed (some slaty limestone with shale partings. Large spring near base)______220± Section of Kinzers formation in vicinity of the Thomasville Stone and Lime Co. quarry 420 + Upper member (in railroad cut south of quarry) : Feet Ledger dolomite (middle quarry) : Hard dense light-blue limestone; weathers to tough White to blue mottled coarsely crystalline dolomite_ 105 + light-buff banded sandstone, stained red in places (sandstone fragments cover top of hill south of Thomasville) ______——__ 20+ (West of road on upland in quarry above river, 50 feet of dark argillaceous to earthy, closely folded Concealed______30 ± limestone makes a horse.) Thin-bedded impure blue limestone with fine wavy siliceous banding which weathers to network of buff Kinzers formation: dense tripoli, and thin dark fossiliferous crystalline Upper member (wall rock) : limestone containing cystid plates and trilobite and Dark slaty, argillaceous limestone and hackly dark shell fragments (pi. 5, A) ___———__—————_____ 50+ dolomite______10 ± Impure shaly limestone (poorly exposed)—___— 30± Thin fissile to platy black earthy shale-______5 Banded, very earthy blue limestone; weathers to fine Earthy-banded blocky sandy limestone; weathers dense siliceous, earthy buff network-_——————— 20± to hard sandstone and to porous sandstone pitted Blue to white impure marble; weathers to buff I anded by solution and removal of limestone pebbles__ 20± tripoli with crystalline cystid plates on surface-— 10 Concealed-______35+ Earthy blue limestone interbedded with purer lime Black fissile shale and slaty limestone______40 + stone at base; weathers to thick-bedded dense earthy Slaty blue limestone and knotty blue dolomite; sandstone______—_————-—— 20 rough bedding surfaces; carbonaceous partings- 25 Blue limestone conglomerate————————————— 5 Earthy dolomite; weathers to tripoli—__—————__ 3 135+ 188 ± Middle member (north quarry) : Dark and light spotted crystalline marble ("leop Middle member : ard rock")______•______10 Concealed (between quarry and railroad cut south of Massive-bedded white coarsely crystalline marble_ 30± quarry). Estimated thickness______40± Dark even-grained limestone with wavy banding; 20 Joiias, A. I., and Stose, G. W., New 'Holland quadrangle: Pennsyl vania Geol. Survey, 4th ser., Topog. and Geol. Atlas No. 178, pp. 11-12, bauds that weather to buff color stand in relief 1926. and contrast with chalky white coating on the ad 21 Jonas, A. I., and Stose, G. W., Lancaster quadrangle: Pennsylvania jacent bauds; basal bed is conglomerate of pebbles Geol. Survey, 4th ser., Topog. and Geol. Atlas No. 168, pp. 26-29, 1930. 22 Stose, G. W., and Jonas, A. I., The geology and mineral resources of fine-grained marble in 'dolomite matrix (tcp beds of the Middletown quadrangle : U. S. Geol. Survey Bull. 840, pp. 28 and in quarry face) ______„„___ 20 34, 1933. Minor unconformity. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRUSt 21 Wrightsville '/a VA- Mile /VI'NTAGE CONESTOGA LIMESTONE, ' K I N Z E R S FORMATION /Upper member,' / DOLOMITE S. Middle ss / Middle member ,'Lowerf South quarry quarry •memb, o«o/y/y8. North quarry Spring ^•Dolomite 100 Feet approx. horse B FIGDBB 8.—Geologic sketch map and section of the limestones north of Wrightsville: A, Map of northern part of Wrighfsville, showing the location of old limestone quarries and revised geologic mapping; B, Section along river bluff north of Wrightsville, showing revised correlation of beds exposed. Middle member—Continued. Feet Partial section of Kinzers formation half a, mile south of White to pink even-grained granular crystalline lime Emigsmlle stone with occasional black blotches; some beds resemble conglomerate (quarry rock, reported to Upper part of formation not exposed. average 98 percent CaCO3 and some beds 99.69 Middle member (exposed chiefly in quarry) : percent) ___—______60 Light-blue hard limestone; much sheared______Knotty blue limestone with maguesian mottling_ Banded light-blue limestone containing cystic! plates 120 ± and other fossils______—_—______Feet Dark massive dolomite______80± Lower member: Laminated mottled limestone; conglomeratic crystal Concealed. Estimated thickness______50 ± line beds contain cystid plates and other fossils Black shale (in hill west of railroad). Estimated (Top of quarry face)-—_——___—______thickness______50 + Concealed______1______30± Tough dense sandy dolomite; weathers to soft buffi porous tripoli or fine standstone_—_____— 20 ± 100± 130 ± 408 ± Lower member (exposed in railroad cut) : Just north of the York quadrangle another good sec Gray platy shale______——_____— 125 tion is exposed in the Pennsylvania Railroad cut half Concealed (shale and sandstone fragments)____— _5± a mile south of Emigsville, and in an adjacent quarry. White saccharoidal dolomite containing many glassy The beds here dip southward 15° and the sequence is quartz grains and weathering to blocky earthy buff inverted, the limestone of the upper part of the forma sandstone, and hard bluish granular quartzite slabs______-______10 ± tion dipping beneath the shale. The sandy beds at the top of the formation are faulted out. 160 ± 22 GEOLOGY OP THE HANOVER-YORK DISTRICT, PA. 20 Strike and dip + F, Fossils X, Abandoned quarry FIGURE 9.—Detailed geologic map of Farquhar Hill and Prospect Hill in York, showing distribution of pure calcic marble and dolomite in middle member of Kinzers formation. Shale on Prospect Hill is lower member, and sandy limestone forming Farquhar Hill is upper member. Fossil localities of Wanner and others in York: 1, Corner of North Penn and West North Streets; 2, Grant Alley and Gas House; 3, Cutcamp's quarry and Smith's lime kilns at Smith and Union Streets. From the detailed sections of parts of the formation the Ledger dolomite. Further stratigraphic work and given on following pages, the general composition of the finding of additional fossils have proved that these the Kinzers formation in the Hanover-York district pure limestones should be included in the middle mem may be stated as follows: ber of the Kinzers formation. General character of Kinzers formation in Hanover-York In many places the mottled limestones in the middle District member of the Kinzers are thick-bedded and very pure, Upper member: Earthy limestones; weather to soft buff containing little magnesium or other impurities, and are tripoli and fine sandstone; generally fossiliferous, and extensively quarried in the vicinity of York ar d Thomas- interbedded with dark argillaceous thin-bedded lime- feet vine. stone———————__———______125-180 Northwest of York in the Willis Creek lowland, many Middle member: Thick white to mottled or spotted mar old quarries are in this pure limestone. The purer high- ble and granular limestone; some coarsely conglom eratic, containing Archaeocyathid reefs and minor calcium limestone has been quarried out, and the rock amounts of dark thin-bedded argillaceous limestone; now exposed is mostly dolomite, which probably replaced earthy generally fossiliferous limestone at base, pure limestone of the Kinzers, and limestone mottled weathers to buff tripoli—______100-175, with dolomite in process of replacement. The sketch Lower member: Dark shale, with earthy limestone map in figure 9 shows the writers' interpretation of which weathers to buff tripoli at the base. (Shale is highly fossiliferous in Lancaster area)______100-150 this area. The dolomite in the quarries is massive bed ded and resembles the Ledger, but the presence of the 325-505 interbedded pure mottled white marble of the middle Because the sandy limestone near the top was be member of the Kinzers formation indicates that this lieved to be the base of the Conestoga limestone, the rock is limestone of the Kinzers that apparently has underlying pure limestone beds in the Palmer Lime and been dolomitized, like that in the Palmer Lime & Cement Co. quarry, the Laueks quarry, and other quar Cement Co. quarry in West York. The following com ries near York were described previously 2S as part of posite section is based on exposures of the pure lime *» Stose, G. W., and Jonas, A. I., op. cit., Bull. 840, p. 28. stone beds of the Kinzers in this area: PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE KA-RTIC OVERTHfttlST 23 Composite section of the limestones in the middle member of the which is exposed in an old quarry at the north end of Kinsers formation in WUlis Creek Valley northwest of York the hill. The rock in this quarry is much broken and Middle member: Feet sheared and the structure appears to be a plunging anti Massive gray fine-grained dolomite (probably replaced cline. The following section is exposed in the quarry: limestone) ; some of it is oolitic and conglomeratic— 20 White and some blue marble; partly oolitic and con Section in old quarry on north side of Farquhar Hill glomeratic, with apparently siliceous dolomite mat rix which weathers to a porous mass standing in White marble—————————_———————————— 5± relief ______15 Impure banded blue limestone; impure layers weather White and blue marble; oolitic in part______30 in relief ______—_—__———————————— 10 ± Massive pure white marble with few wavy dolomitic Conglomerate of white marble fragments in blue and bands; weathers to granular surface_—_____ 30 white banded and streaked marble———:———————— 20± Granular white marble; some massive thick-bedded Massive granular dolomite; in part oolitic——————— 20 ± conglomerate; weathered surfaces have a thick Blue and white streaked fine-grained marble—————— 30 ± dark porous coating___———______—___ 30 White marble, with blue bands; wavy dolomitic 85 ± bands weather hi relief __—______15 Marble (poorly exposed)______10 Farquhar Hill is apparently cut off on two sides by White marble, in part banded and mottled with blue__ 20 faults. The sketch map (fig. 9) shows locations where 170± Wanner and others collected an interesting assemblage Lower member: Dark shale. of Lower Cambrian fossils. Most of the marble layers are limestone and not In the area south of West York the thick limestone of dolomite. the middle member of the Kinzers formation has Hen Farquhar Hill (fig. 9) is composed of the sandy upper extensively quarried by the Palmer Lime and Cement member of the Kinzers formation and is apparently Co. The quarries are indicated on the sketch map of the underlain by the pure marble of the middle member West York area (fig. 10). A sketch plan and cross sec- Cpnestoga limestone Ledger dolomite Sandy limestone Limestone Vintage dolomite Fault T, Over-thrust side D, Downthrow U, Upthrow !!»<(, IE Klippe ./!>,,<• ^^ *sy Strike and dip © Horizontal beds + F, Fossils uarry FIGUBE 10.—Geologic map of West York and vicinity, showing detailed geology and structural interpretation. Fossils were collected by Wanner at point F. Location of quarries: 1 and 2, active quarries of Universal Gypsum & Lime Co.; 3, abandoned quarry of Palmer Lime & Cement Co.; 4, abandoned quarry; 5, active quarry of Eli Zinn Co.; 6 and 1< abandoned and active quarries of Eli .Zinn Co.; 8, active quarry of York Stone & Supply Co. 24 GEOLOGY OB* THE HANOVER-YORK DISTRICT, PA. Thick light-gray crackled dolomite; irregular bed at Feet top of south face of quarry—————————______10-20 Massive tough dark-blue mixture of limestone ani dolomite; face and floor at south side of quarry__ 40± 120-150± In this quarry, pure high-calcium limestone grades upward through beds of mottled limestone to coarse granular dolomite, which forms the top of the north face of the quarry (pi. 5, B). Along joint fractures and associated brecciated zones in the pure limestone (fig. 12), the rock merges laterally into irregular masses of coarse-grained grayish dolomite. Obviously, circulat ing waters have gradually changed the original pure Horizontal high-calcium limestone to dolomite. In places, pure Strike and dip dark-blue fine-grained high-calcium limestone that was not dolomitized has been metamorphosed to. a coarse grained white marble. At the border of such altered Anticline rock, a transition zone of mottled blue and v^hite mar ble is composed of rounded residual masser of dark- blue limestone in white marble. The unaltered blue masses resemble pebbles in the coarse-grained marble, SE. Fault- and the rock may be mistaken easily for a limestone con NW. glomerate. Coarse-grained dolomite, resulting from the addi tion of magnesium oxide and the recrystallization of the limestone, closely resembles the overlying Leiger dolo mite; and the two dolomites cannot be distinguished FIGDRH 11.—Sketch of plan and section in quarry of Universal Gypsum except by the association of key beds. TT e coarse- & Lime Co. in West York: A, Plan showing general anticlinal struc ture of quarry rock and a fault cutting across the quarry; D, down- thrown side. B, Generalized cross section of southwest face of quarry ; scale twice that of map. All limestones are in middle member of Kinzers. Calico rock is marble mottled with magnesium carbonate. tion of the large active quarry now operated by the Universal Gypsum and Lime Co. is shown in figure 11. The general structure is a gently plunging anticline cut by a fault which passes through the northern part of the quarry. The limestone in the Universal Gypsum & Lime Co. quarry are in part magnesiaii and in places are com pletely altered to dolomite. A general section of the beds exposed in the quarry follows: Section of limestones of the middle member of the Kinzers forma tion in quarry of Universal Gypsum & Lime Company Gray well-bedded dolomite and thin blue fossiliferous Feet w. limestone (exposed northwest of plant)______15 Coarse granular dolomite; weathers to granular sur face ; forms top of north face of quarry; much thicker in places, owing to replacement of pure lime stone by magnesium carbonate diagonal to the bedding______—______5 Blue and white streaked pure marble-______5 Thick-bedded white sugary marble with a few dark coarsely crystalline blotches______20-40 White marble mottled with magnesian spots and bands FIGDEE 12.—Sketches showing dolomitization of limestone in quarry of Universal Gypsum & Lime Co. in West York: A, Brecciation and (pi. 5, B, Calico rock; reported to contain 18 percent dolomitization of limestone adjacent to fault in west wall; B, Part of magnesium carbonate) ; magnesian spots weather in north wall of quarry showing irregular replacement of white marble relief and to chalky white blotches.-______25± by dolomite. GEOLOGICAL SUHVEY PHOFESS1ONAL PAPER 204 PLATE 5 J A. RETICULATELY WEATHERED ARGILLACEOUS BANDED LIMESTONE OF UPPER MEM- B. WEATHERED SURFACE OFJMOTTLED LIMESTONE (CALICO ROCK) IN MIDDLE MEMBER BER OF KINZERS FORMATION IN RAILROAD CUT SOUTH OF QUARRY OF THOMASVILLE OF KINZERS FORMATION, EXPOSED IN QUARRY OF UNIVERSAL GYPSUM & LIME CO. STONE & LIME CO. WEST YORK. Beds generally fossiliferous. C. STRUCTURE IN LIMESTONES OF KINZERS FORMATION IN ABANDONED QUARRY OF D. FAULT IN KINZERS FORMATION EXPOSED IN QUARRY OF YORK VALLEY LIME & STONE PALMER LIME & CEMENT CO., WEST YORK. CO., 6 MILES NORTHEAST OF YORK. Illustrated in figure 13. Thin black dolomitic bed, which bends downward, is apparently overlapped un- White marble thrust over dark argillaceous limestone and shale at left. Fault plane dips 60° S. (to the right). conformably by horizontal beds. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRTJST 25 NW: SE. Pure dove limestone -H ^-~-——————————————-L-*J—L-J—j-' i i i i i ir i i j « 6 Dark dolomite i—C f.nn <5 Inmo r a+!/- mat- (DO Conglomeratic marble (Slickensided surface) Fault face 6 Dark dolomite Residual mass \ .1 m u i i i i i i M 11 111 i i 11 i i m i n i i i L A 25 feet, approx. SE. NW. ,6 Dark dolomite B N. 'Calcite vein <^ o 'r White marble FIGURE 13.—Sketch of plan and sections in abandoned quarry (No. 3 in fig. 10) of Palmer Lime & Cement Co. in West York: A, Plan and walls showing down folding of thin lay^r of dark dolomite, a residual mass of which is preserved in bottom of quarry. Irregularity of, sedimentation and overlapping of beds after folding or slumping are indicated in southeast face land in east corner, which is shown in sketch of northeast face. Northeast face of quarry seems ^:o be a fault plane. B, Section diagonally through quarry to east corner. C. Detail of downfolfl in the thin dark dolomite bed in east corner of the quarry. Dove limestone at top seems to Overlap downfolded beds. Gray limestone recrystallized into irregular patches of white marble shc(wn at right. 462857—44 26 GEOLOGY OP THE HANOVER-YORK DISTRICT, PA. grained dolomite in Willis Creek Valley north of York the breccia and lapped over the older'beds on the sides of (fig. 9), as previously mentioned, closely resembles the depression (fig. 13> A and B). Later, the blue lime Ledger dolomite; but these rocks are intimately asso stone was in part recrystallized into a white marble, as ciated with high-calcium mottled marble of the Kinzers shown in figure 13, C'. A 6-inch layer of dark impure formation and are not separated from them by the dolomite is the key bed in deciphering the structure. sandy, earthy limestones usually present at the top The southeast wall shows the irregularity of sedimenta of the Kinzers formation. For these reasons, the tion. The 6-inch key bed of dark dolomite is apparently dolomite is mapped as part of the Kinzers. downfolded and thinned. The top bed of pure dove Earthy ss. Limestone 1 ^Conglomerate limestone income, rate e marWe /Q-2Q T/O-2O L JWC0£ AS H/GHWA Y A FIGUBH 14.—Sketch of plan and sections in quarry of York Valley Lime & Stone Co., 6 miles north east of York: A, Plan showing fault cutting east side of the quarry and another fault, which appears to form the back wall. Fossils were collected at two points marked F. B, Cross section of the quarry, scale three times that of plan, showing the faults and location of the fossiliferous bed. C, Detail of relationships at the fault contact on east side of quarry. Residual masses of white marble are enclosed in the slate at the contact. In an abandoned quarry of the Palmer Lime and Ce limestone shows similar dowrifolding and overlapping ment Co. (No. 3 in fig. 10), near Codorus Creek and of beds. The 6-inch key bed is sharply downfolded southeast of the road to Highland Park, are exposed in an unquarried mass in the northeast corner. (See some remarkable sedimentary structures, which appar pi. 5, C.) The northeast wall exhibits a horizontally ently resulted from the caving and settling of beds dur bedded limestone, veined, brecciated, stained red and ing deposition. The lower beds of blue limestone ap cut by slickensided joints, which suggest a fault. As parently sank and the depression was filled with marble shown in the photograph, plate 5, #, the top bed of breccia, which is shown on the northeast wall of the pure dove limestone appears to lap over this breccia, quarry and was the chief rock formerly quarried. Pure indicating deposition after the downfolding and the dove limestone and dolomitic beds seem to have capped subsequent filling of the basin with breccia. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRTJST 27 The purer limestone beds of the Kinzers formation Thin, platy fine-grained, argillaceous limestone with slaty Feet are well exposed in the quarry of the York Valley Lime partings______'.-_____—______——— 20± Thin-bedded dark argillaceous granular limestone contain & Stone Co., 6 miles northeast of York and just north ing Nisusia festinata and Bonnia sp., dark mud-lump of Lincoln Highway (U S 30). A thrust fault passes earthy limestone, and some beds of limestone con through the quarry, and the limestones of the Kinzers glomerate______-:—_—————————'.—— 40± formation to the south are overthrust on other lime Beds of coarse limestone conglomerate interbedded with stones of the same formation. A sketch map of the dark-blue crystalline limestone, weathering white; and quarry and a cross section are shown in figure 14. thin-bedded to shaly black earthy limestone or calcareous argillite______.______— 30± Massive blue argillaceous crystalline limestone, weather Partial section of the Ein-zers formation south of fault in York ing dull gray, and light granular crystalline limestbne— 20 ± Valley Lime & Stone Co. quarry 6 miles northeast of York Limestone conglomerate composed of 1-inch granular Feet crystalline marble pebbles in dark argillaceous limestone Thick granular, crystalline gray finely conglomeratic lime matrix; some dense dark crystalline limestone beds—— 30-t stone containing cystid plates and stem segments; inter- Thick black earthy crystalline limestone, weathering dull- bedded thin, platy dark argillaceous limestone with gray,-and lighter purer crystalline limestone with fine earthy shaly partings, contains shells (Nisusia festi- conglomerate composed of granular limestone pebbles nata) at west side of quarry______25 and scattered glassy quartz grains————————————_ 20± Black earthy finely conglomeratic limestone; coarsely oolitic to pisolitic; at base, pebbles of underlying white 245± marble————______10± Massive-bedded white marble; basal beds, a conglomerate Partial section of Kinzers formation in old quarry north of containing thin flat pieces and larger rounded frag Philadelphia St., near Harrison St., in East York ments of white marble______30± Feet White to blue crystalline limestone and thin laminated Bluish granular pitted limestone——————————_—__ 15 limestone and conglomerate containing glassy quartz Bluish limestone banded with dark argillaceous partings— 3 grains———_———______20± Massive white saccharoidal marble and blue dense fine Black shale and interbedded thin-bedded granular, cry grained limestone merging into one another (main stalline finely conglomeratic fossiliferous limestone con quarry rock)——————————————————————————— 50± taining Nisusia festinata with earthy, argillaceous rip Pure chalky white coarsely crystalline marble; lenticular; ple-marked partings; an anticline of this lower bed is merges into argillaceous blue limestone that weathers to. overthrust on other limestone of the Kinzers formation; buff earthy shaly rock——————————————————— 5 fault contact at east arm of quarry. (See fig. 14, C and Coarse conglomerate .composed of large fragments ol pi. 5, D.) ______25± chalky white marble, pitted granular limestone, and slabby bluish granular limestone containing crinoid seg 110± ments, in buff argillaceous finely conglomeratic matrix; fluorspar on shear planes———————————————___ 20± North of the fault in this quarry, thick alternating Blue limestone with wavy buff argillaceous partings-—— 10± beds of limestone and limestone conglomerate were Pure granular pitted white marble with layer of blue and thought at first to belong to the Conestoga limestone,24 gray banded argillaceous limestone______15± but interbedded platy argillaceous limestones containing Nisusia festinata and Bonnia sp. indicate that the rocks 188± are part of the Kinzers formation. At the north side Another partial section of these beds in East York of the quarry, between these limestone beds and the follows: earthy sandstone at the top of the formation which lies Partial section of Kinsers formation in A. M. Hake quarry at north of quarry, there is apparently another fault. This Philadelphia and Center Sts., East York section follows: Feet Blue fine-grained thin-bedded limestone containing some Partial section of middle member of the Kinsers formation north quartz grains; rhythmically banded by thin argillaceous of fault in York Valley Lime and Stone Co. quarry partings __——————__———————————————————— 30± (Irregular contact with underlying mai?ble owing to flow Feet Banded limestone with beds of granular, crystalline lime of the marble under intense compression) stone containing cystid plates and stem segments; inter Thick-bedded white recrystallized marble mottled with bedded dark argillaceous limestone, with shaly earthy dark gray_—_———————————————————————— 20± partings contains Nisusia festinata-——_—_—__ 25± Blue pure limestone with some fine argillaceous partings; Conglomerate composed of white marble pebbles in buff thick beds of coarse conglomerate composed of white magnesian matrix containing cystid stem segments; granular marble—some larger masses more than 10 also blue and white marble conglomerate___—_ 20± inches thick—containing glassy quartz grains and crin Conglomerate composed of dolomite pebbles______20± oid stem segments, in dark limestone matrix__—_— 50 ± Dense granular dolomite containing scattered glassy quartz Earthy limestone weathering to porous tripoli of buff to red grains_____————————————————______20± color_____——————————————————————_—— 2 (Beds above exposed only on west side of quarry) Limestone and earthy weathering beds————_—————— 10± ^Stose, G. W., and Jones, A. I., op. cit. (Bull. 840), pp. 28 and 34. 112 ± 28 GEOLOGY OP THE HANOVER-YORK DISTRICT, PA. Earthy fossiliferous limestone beds directly above the shale of the lower member are well exposed at an old quarry one-eighth of a mile north of Myers Mill, just east of the preceding section. The beds here are overturned. Partial section of the Kinsers formation at quarry near Myers Mill, Middletoicn quadrangle Middle member: Feet Dark-blue crystalline limestone; black shells of Salterella and fragments of trilobites abundant—__ 5 B Dark-blue shaly impure limestone weathering earthy FIGURE 15.—Sections across the A. M. Hake quarry in East York: A, (in small quarry below road and exposures above Sketch showing anticlinal structure exposed during the operation of road)______30± the quarry in 1921; B, Detail of anticline. Dark limestone breccia cemented by buff dolomite; weathering results in lumpy conglomeratic appear The beds in this quarry appear to dip southward ance______—_———_—————_——————— 5 20°-40°, but the quarry at a former stage showed an Dark lenticular limestone with irregular buff earthy anticline in the middle. (See fig. 15.) dolomite layers producing a wavy mottled banding The Laucks quarry near Springdale School, 2 miles and spotted appearance ("leopard rock")_——— 10 Impure shaly gray limestone containing some earthy northwest of York, exposes 15 feet of white saccharoidal fossiliferous bands (in small quarry above road) _— 20± marble with few coarser dark blebs and, at the top, Thick dense, tough earthy dolomite with black streaks; magnesian layers. Drill cores extending to a depth of weathers to thick slabby porous tripoli; highly 240 feet show similar white marble with gray mottling. fossiliferous (top of quarry)_-______6 This stone is reported to have an average of 95 percent 76 ± or more CaCCk The marble from some of these cores Concealed interval. was tested for ornamental stone and took an excellent Lower member: Shale (on hill to south). polish. Fossiliferous earthy limestones are also erposed in a Partial section of middle member of the Kinsers formation in quarry in the extreme northwest corner of the York the Ell Zinn quarry, north faee of Green-mount Cemetery Hill quadrangle on the highway (U. S. Ill). The section, (No. 8, fly. 10) Feet the beds of which are also inverted, follows: White marble______—_—— 30± Dark argillaceous limestone-_—______-__— 5± Partial section of the Kinsers formation, northwest corner of Finely banded white marble containing spongelike fossils York quadrangle (archaeocyathids) ______—_—_ __—-———-— 30 ± Middle member: Feet Dark dense argillaceous limestone——______————— 15 ± Black crystalline limestone; black shells of Salterella Massive white granular marble———————_——————— 30± and fragments of trilobites abundant______10 Dark wavy banded argillaceous liinestone______30± Dark shaly limestone (poorly exposed)______— 20± Blue limestone (quarried) ; largely mottled and1 wavy 140 ± banded with argillaceous impurities (in part white spotted marble or "leopard rock") and som^ blue Partial section of the middle member of the Kinsers formation pure limestone ______— 40± on road southeast of Kohlers Hill Tough yellow earthy dolomite with black streaks and Blue and white mottled fine-grained marble ("leopard feet thick tripoli beds; fragments of trilobites anc1 other rock")______3 fossils abundant______10± Concealed______10 ± Dense earthy tripoli, and buff sandstone banded with 80 ± black argillite streaks______10 ± Concealed interval. Concealed______20± Lower member: Shale (on hill to south). White crystalline marble______2 Concealed______•______15 ± Partial section of middle member of the Kinsers formation in Pink to white fine-grained marble with knotty earthy Eli Zinn & Co. quarry on east face of Greenmovnt Cemetery banding ("leopard rock") which weathers to earthy net Hill (No. 7, fig. 10) work ; contains SaltcreU-a______20± Feet Dense impure limestone;* weathers to buff tripoli and Thick-bedded (3-foot beds) dense earthy tripoli; bluish dense earthy limestone where fresh; contains Salter- earthy sandstone; contains trilobites and brachiopods- 2 Blue and white marble with magnesian layers that weather ella —_—_—______10± Light-blue limestone with wavy argillaceous banding ; con into wavy bands; at base, "leopard rock" and co^lom- erate composed of large white marble blocks ard con tains crinoid plates______.______10 taining cystid plates____—______6 Hackly gray to buff shale______15 Concealed—______,__ 45 ± Earthy light-blue dense limestone; weathers to dense Dark knotty magnesian mottled limestone______5± tripoli __———„__——————_—_——______9 Banded light-gray magnesian limestone in 2 thick beds; 165 ± irregular fucoid-like magnesiau banding______20 PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRTJST 29 Highland Park Eli Zinn quarry Highland Park NW. Eli Zinn quarry FIGURE 16.—Sections along Codorus Creek at the Eli Zinn quarry in southern part of York: A. Sketch of north bank of the creek. Sandy beds of upper member of Kinzers formation cap High land Park Hill at top of quarry, which exposes an anticline of the middle member. Coarse-grained marble of middle member makes the rock pinnacle west of fault B, Cross section ^through quarry, showing fault north of quarry. Dark impure limestone with buff banding in 1- to 2-inch Feet overlain by 20 feet of black platy slate and banded sandy beds; weathers to argillite______15 shale. A fault is exposed in the stripped area just west Light-gray fine-grained marble in 2-iuch beds; weathers to of the quarry. (See fig. 16, B.) Wanner reported ex blue marble mottled with buff niagnesian layers and coarse granular upper surface______12 cellent specimens of trilobites (Olerwides cf. 0. Marconi Massive light-gray granular, crystalline dolomite contain Whitfield) from loose pieces of slabby sandstone west ing dark specks (probably replaced limestone)____ 15 of the fault. Walcott 25 described the fossils and re ferred to the quarry as the Highland Park locality. 79 Partial section of Kinsers formation in Eli Zinn & Company Section of part of Kinsers formation in old quarry on north slope quarry, Codorus Creek, south of Highland Park in West of Farquliar Hill in York York Feet Upper member: Hackly buff earthy shale, slabby sand Upper member: Feet stone, and porous tripoli (forms top of hill)______20± Black, banded earthy shale______20± Dense dark-banded glistening argillaceous sandy lime Middle member: stone ; weathers to buff-banded earthy sandstone White marble (largely concealed)______30: blocks______10 Blue limestone with niagnesian mottling which Thin-bedded dark nodular to shaly limestone, banded weathers in relief______10 with impurities ; contains pyrite cubes—______10 Wary banded, white, pink, and blue marble, in part Dense, tough light-blue, banded finely siliceous lime conglomeratic; dolomite at top______15 stone ; weathers to fine buff sandstone______8 Rounded white marble residual masses in dolomite matrix___=______2 Light-gray massive granular dolomite (probably a Middle member: replaced limestone). Dark-gray argillaceous limestone with gray magnesian banding; lighter gray below______52. 57 + Very thin-bedded dark glistening slaty limestone; The Eli Zinn Co. quarry on Codorus Creek, south of weathers to shaly fragments—_———————_——_ 8 Highland Park in the southern part of York (No. 5 in Gray and white mottled marble-——______20 fig. 10), exposes the upper part of the Kinzers formation. An anticline in the quarry brings up 20 feet of pure 80 dove-colored marble, which underlies 60 feet of thick- A section of the upper sandy member of the Kinzers bedded banded blue agrillaceous limestone, both belong formation along the Dover road over the Greenmount ing to the middle me'mber of the Kinzers. (See fig. 16.) Cemetery Hill follows. The sketch (fig. 17) shows the About 30 feet of light and dark rhythmically banded minor folding of these beds. earthy, sandy, and argillaceous limestones, containing 25 Walcott, C. D., Cambrian rocks of Pennsylvania, U. S. Geol. Survey abundant bright pyrite cubes, cap the quarry and are Bull. 134, p. 18, 1896; and personal communication from A. Wanner. 30 GEtOLOGT OF THE HANOVER-YORK DISTRICT, PA. Partial section of Kinzers formation along road on northwest (Bonnia sp.) were obtained in some of the beds. An slope Greenmount Cemetery Hill, 1 mile north of West York other fault, not shown in the sketch, is exposed in the Upper member: Feet railroad cut east of the quarry. The quarry h in massive Buff dense, tough tripoli or fine sandstone; banded light-gray mottled crystalline limestone, overlain by near top; at base, thicker denser sandstone beds, thin-bedded dark argillaceous limestone with thick black 3 to 5 feet thick, derived from the weathering of light blue fine-grained quartzose limestone_____ 20 carbonaceous shale partings and thin shale beds that Buff porous blocky sandstone (surface of hill covered show wavy bedding and ripple marks. Some of the thin- with blocks)______—___—___—__— 5± bedded rock is crystalline and f ossilif erous. At the west Dark earthy to sandy shale___—_—_____————— 10± side of the main quarry, the shale and thin-bedded ar gillaceous limestone are faulted down alor.g a nearly 35± vertical plane. At the east side of the quarry, an over Middle member: Thick fine-grained white marble and dark turned anticline of the thin-bedded limestone is thrust dolomite. over the thick beds. (See fig. 18.) West cf the main The sandy beds of the upper member of the Kinzers quarry, recent stripping has exposed another nearly formation are exposed also on another hill two miles vertical fault (fig. 18, A). Trilobites have been ob southwest of West York. tained in thin beds of limestone at this locality. Partial section of Kinzers formation along road on hill north Partial section of Middle member of Kinzers formation in Roy of Lincoln Highway at Hellam, Middletoion quadrangle Bittinger quarry icest of Spring Grove Feet Conestoga limestone: Dark-banded calcareous slate in rhythmically repeated Coarse limestone conglomerate______5± 3-foot beds with ripple-marked surfaces and black carbonaceous partings; upper beds 6 inches thick; Kinzers formation: broken by diagonal cleavage dipping eastward_____ 25± Upper member: Dark calcareous shale and interbedded thin crystalline Buff tripoli; derived from earthy dolomite.___ 20 ± fossiliferous limestones______4 Black banded dry earthy slate; contains small Dark argillaceous limestone with black shale partirgs__ 4 pyrite cubes in places_—_—_—_____ 20± Massive light and dark mottled granular, crystalline mar Slabby tough calcareous sandstone, buff colored, ble; top layer has wavy surface coated with black banded, and mottled with dark gray; thin black carbonaceous film______20 argillaceous slaty partings (makes low ridge) _ 30± 70+ Partial section of Kinzers formation in Stoners quarry 1 mile At the J. E. Baker quarry at Thomasville, the pure ea$t of Columbia, Lancaster quadrangle limestone of the middle member contains m^ny needle- like crystals of quartz which in places on the surface Kinzers formation: - Upper member: Feet weather out into dense nests of crystals (pi. 6, 0). Even-layered dark calcareous shale or argillite; AGE AND CORRELATION weathers to porous light-weight bony, platy shale —_——_———————————_—————_— 3 The Kinzers is the most fossiliferous formation in Coarsely granular marble; weathering shows York County. Fossils have been collected from all three round limestone pebbles at base—___——___ 4 Earthy dolomite; weathers to buff bony tripoli members of the formation. A few feet of earthy beds enclosing marble pebbles-—_—_—_——__ 3 at the base of the shale of the lower member contain the lowest fossiliferous horizon. Fossils obtained by the 10 writers and C. E. Eesser from these beds at Donnerville, Lancaster County, have been identified by Resser as Middle member: Coarsely granular glistening dark and light mot Bonnm senectaf (Billings) and Olenetkis sp. (frag tled marble; weathering shows round pebbles- 20 ments). Shaly dark limestone————————______5 The shale of the lower member is highly fossiliferous, Light-gray massive limestone, and conglomerate especially in the vicinity of Lancaster. A complete of granular gray limestone in dark limestone list with descriptions and plates of fossils frcm the shale matrix———______—____———____———__— 20 ± Thin-bedded dark argillaceous limestone with member in Lancaster and York counties i" given by crenulated shiny argillaceous partings, and Eesser and Howell in a recent publication.26 These granular limestones in beds 4 inches thick___ 20 ± fossils were collected from four localities in Pennsyl vania, three of which are in Lancaster Connty. The 65 ± fourth is located 2 miles north of the square in York, The Roy Bittinger quarry, west of Spring Grove, where fossils were collected largely by C. D. Walcott, shows normal faulting, folding, and overthrusting (fig. 26 Resser, C. E., and Howell, B. P., Lower Cambrian Olvnellus zone of 18 and pi. 6, A and B) ; and good specimens of trilobites the Appalachians: Geol. Soc. Am. Bull., vol. 49, pp. 205-248, 1938. PALEOZOIC SEDIMENTARY ROCKS NORTH OF -THE MARTIC OVERTHRTJST 31 GREENMOUNT CEMETERY NW. HILL FIGURE 17.—Section along Dover road over Greenmount Cemetery Hill, showing structures in sandy limestone of tfpper member of Kinzers formation. NW. NW. SE. NW. PIGOBB 18.—Sections in Roy Bittinger quarry west of Spring Grove: A, Sketch of north bank of Codorus Creek, showing two normal fruits and a thrust fault. At points marked F, fossils were collected In thin-bedded crystalline limestone overlying massive granular marble of middle member of Kinzers. B, Detail at the normal fault exposed in quarry. The massive-bedded marble is overlain by dark argilla ceous limestone and shale, and this by thin-bedded fossilerous limestone, which is cut by diagonal cleavage that dips southeast. C, Detail of structure at thrust fault exposed at right edge of quarry. Charles Schuchert, and Atreus Wanner many years ago. Paedeumias eboracense Resser and Howell Most of the species, however, occur also at the localities Wanneria walcottana (Wanner) Bsmeraldina macer (Walcott) near Lancaster. The fossils found 2 miles north of Bonniella yorkensis Resser and Howell York include the following: Anomalocaris lineata Resser and Howell Lepidocystis wanneri Foerste Resser and Howell regard this fauna as the equivalent Salterella acervulosa Resser and Howell of that from the lower shales of the Parker slate ex Hyolithes wanneri Resser and Howell posed in the Parker quarry, near Parker Cobble, Vt. Eoagnostus roddyi Resser and Howell The Parker slate was first described and named by Olenellus similaris Resser and Howell Olenelhis alius Resser and Howell Keith.27 Schuchert 2S gives a more complete description Olenellus wanneri Resser and Howell aT Keith, A., Stratigraphy and structure of northwestern Vermont: Jour. Wash. Acad. Sci., vol. 22, p. 371,1932. Paedeumias glabrum Resser and Howell 38 Schuchert, Charles, Cambrian and Ordovician stratigraphy of nerth- Paedeumias yorkense Resser and Howell western Vermont: Amer. Jour. Sci., 5th ser., vol. 25, pp. 362-364, 1933. 32 GEOLOGY OF THE HANOVEK-YORK DISTRICT, PA. of the formation, including the impure dolomites and beds in the upper member of the formation at many reef limestones above the slate, and lists the fossils from places indicated on the geologic map of the district, and the Parker slate. at several places in the adjoining Middletown quad Resser and Howell 29 correlate the shale member of the rangle. Fossils collected a quarter of a mile north of Kinzers formation with the Rome formation because Strickler Station were identified by Resser as Agnostus, both contain Olenellus and Hyolithes. The writers' ob Bonnia, Nisusia, an unnamed phyllopod, and Salterella. jection to this correlation is fully stated in their paper30 Those collected on the road to Highmount north of on the Austinville area, Va., and will be restated in the Lincoln Highway, l1/^ miles northeast of the center of discussion of the Great Valley facies and its south Hellam, were identified as Eoagnostus, cystid plates, and eastern limestone facies. (See p. 34.) an alga resembling Morania. Schuchert reported Acro- Just above the shale, earthy limestones at the base of thele decipiens from this locality. The writers' largest the middle member have yielded fossils near Myers Mill collection of fossils at, this horizon was obtained from ex in the Middletown quadrangle, from the quarry at the posures on the Western Maryland Railroad, south of the northwest corner of the York quadrangle, and near quarry of the Thomasville Stone and Lime Cc, These Rohrerstown in the Lancaster quadrangle. Collections were identified by Resser as Syspacephalus?, Kochiella, by the writers and others were identified by Resser and . Nisusia, Hyolithes, cystid plates, and a Discina like form include: probably Paterina. Nmma, Yarkia, and undetermined trilobites were collected at Sunnyside Station on the Nisusia festinata (Billings) Kutorgina cingulata (Billings) York Electric Railroad half a mile southwest of Bair. Paterina bella (Billings) » In the limestone quarry of Roy Bittinger, at the rail Kootenia marcoui (Whitfleld) . road southwest of Spring Grove, good specimens of Dawsonia parkeri (Walott) trilobites were collected by the writers and by Josiah Rustella edsoni Walcott Bridge and were identified by Resser at Bonnia cf. B. Yorkia wanneri Walcott Kochiella? Pennsylvanica Resser capito. Paterina sp. was also collected her?. In a Periomella roddyi Resser small quarry 1 mile southeast of Thomasville, Nisusia, Ptychoparella lancastra Resser Kootenia, and Ptycoparella were collected. In the Ptychoparella sp. quarry on the east side of Greenmount Cemetery Hill, Hyolithes sp. Nisusia, Kutorgina, and cystid plates were collected; Olenellus sp. Bonnia bubaris Walcotl and 2 miles southwest of West York, Periomella sp., and Bonnia carito Walcott Eoagnostus sp. were obtained. Cystid plates About 1895 Atreus Wanner, Charles Schuchert, and Salterella sp. C. D. Walcott collected trilobites and other fossils from Fossils collected by the writers from a higher argilla sandy shale near the top of the Kinzers formation in ceous limestone in the middle member at the quarry of the northern part of York. These fossils were reported the York Valley Lime & Stone Co., 6 miles northeast of from three localities: in Grant Alley near tH plant York, were identified by Resser as Kochiella sp., Agnos of the York Gas Co., at Cutcamp's quarry and Smith tics sp., Ptychoparella sp. [Ptychopana], Prozacan- lime kiln north of Cottage Hill Road, and at Fenn and thoides sp., Nisusia festinata (Billings), Lingulella sp., North Streets. (See fig. 9.) Only the Grart Alley and a phyllopod resembling Schaefferia. G. A. Cooper locality can be studied at present because of the city's and the writers also collected Kootenia sp. from these development, and the writers have recently collected beds. a number of fossils from this locality. The fossils in The purer limestones and marbles of the middle mem the following list from this horizon were identified by ber, extensively quarried in the area, are generally un- Resser: fossiliferous, but the writers have observed archaeocy- Acrothele decipiens (Walcott) Acrothele yorkensis (Walcott) athid reefs in these beds at the Forry Lauck's quarry just Poliella LBathyurlscnsl bala (Walcott) south of Lauck School, at Eli Zinn quarry on the north Agnostus sp. slope of Greenmount Cemetery Hill, and in the quarry Ptychoparella sp. of the Universal Gypsum and Cement Co. in West York. Chancia n. sp. Similar archaeocyathid reefs occur in pure marble and Chancelloria yorkensis (Walcott) Periomella yorkensis Resser limestones of the same age near Austinville, Va., (see Prozacanthoides sp. p. 33). Cystid plates The writers collected fossils from the earthy, sandy 'In the report on the Middletown quadrang1'?,31 the 2» Resser, C. H., and Howell, B. F., op. cit.. p. 205, 1938. writers assigned these fossils to the Ledger dolomite 30 Stose, G. W., and Jonas, A. I., A southeastern limestone facies of Lower Cambrian dolomite in Wytlie and Carroll Counties, Va.: Virginia 31 Stose, G. W., and Jonas, A. I., Geology of the Middletown quad Geol. Survey Bull. 51-A, pp. 20-22, 1938, rangle, Pa.: U, S, Geol. Surv. Bull, §40, p. 29,1933, GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 6 B. THRUST FAULT IN ROY BITTINGER QUARRY, SPRING GROVE. Dark argillaceous limestone thrust westward (to left) over thick-bedded granular limestone. (See fig. 18, C.) ^. VERTICAL NORMAL FAULT IN ROY BITTINGER QUARRY, SPRING GROVE. Dark thin-bedded argillaceous limestone at left is faulted down relative to thick-bedded granular limestone. Both limestones ate part of the Kinzers formation. (See fig. 18, A and B.) C. NESTS OF NEEDLELIKE CRYSTALS OF SMOKY QUARTZ ON WEATHERED SUR FACE OF LIMESTONE IN KINZERS FORMATION IN SOUTH QUARRY OF J. E. BAKER CO., THOMASVILLE. PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRTJST 33 because Resser considered them to be high in the Lower purities, except in one cherty layer. The dolomite is Cambrian or in the Middle Cambrian. very thick bedded, coarse grained, and of light-gray Similar fossils, including PolieUa bala, were collected color, mottled in places with dark spots. It weathers by the writers from the upper part of the Kinzers for to a characteristic deep-red granular soil. The chert mation in the Pennsylvania railroad cut at Dillerville, horizon is near the top of the formation and is mappec1 west of Lancaster. in the Hanover quadrangle from West York to beyond All the fossils collected from the Kinzers formation Botts. Residual porous masses of chert occur in the indicate Lower Cambrian age. The name, Kinzers for deep-red dolomitic soil and in places are so concentratec1 mation, has been recently extended 32 to a fossiliferous as to make hills. The beds above the chert horizon are series, which is lithologically and faunally similar, in a deeply weathered but are of the same character as the small area south of Austinville, Va., on the southeastern dolomite below the chert. edge of the Great Valley. The fossils collected there The dolomite is so pure that elsewhere in the regior are listed on pages 15-18 of the bulletin referred to. it is extensively quarried for magnesian products, but The fauna from Fossil Point in the Virginia area is has not been utilized for this purpose in this district described by Resser 33 as similar to that in the middle or in adjacent areas. The old quarry of the Dolomite member of the Kinzers formation in the vicinity of Products Co. at Shreiner, 3 miles northwest of JLan- York. The rock at Fossil Point is a pure white crystal caster, is the nearest locality where it has been quarried line limestone, with thin earthy-weathering layers con for magnesian products. At Billmeyer, on the Susque- taining archaeocyathid reefs in several beds and abund hanna River in the Middletowii quadrangle, J. E. Baker ant Lower Cambrian brachiopods and trilobites. Ac and Co. quarry and deadburn the dolomite for the lin cording to Resser fossils, including PolMla ~bala, col ing of basic open-hearth furnaces. Large quarries in lected from the top of the middle member of the Kinzers the Ledger dolomite are operated by the Warner Com in the Virginia area, possibly belong to the same fauna pany at Cedar Hollow and Mill Lane, 5 miles south as those, from the uppermost earthy-weathering sand of Phoenixville; and there are many more quarries ir stones of the upper member in Grant Alley near York. the vicinity of Schuylkill River south of Norristown. Resser states also that the Bonnia fauna of the Kinzers near York and southeast of Austiiiville, Va., is the same The total thickness of the formation can not be de as that from the Forteau 34 limestone of Bonne Bay, termined in the Hanover-York district as the top ir Newfoundland. not exposed. North of Marietta in the Middletowr area, where the Elbrook limestone overlies the Ledger LEDGER DOLOMITE dolomite north of the Chickies overthrust, a thicknesr NAME AND DISTRIBUTION of 1,200 feet has been computed from the width of the outcrop and average dip. The Ledger dolomite was named from the village of Ledger, Lancaster County, Pa., where it is typically _ AGE AND CORRELATION exposed and is overlain by the Elbrook formation north of Lancaster. In the Hanover-York district this dolo No fossils have been found in this formation in thi? mite is not found everywhere above the Kinzers forma district. Fossils previously mentioned as occurring ir tion because in many places the Conestoga limestone the Ledger dolomite are now known to come from the overlaps on the Kinzers formation. The Ledger is Kinzers formation. The pure limestones with impure best exposed in the area north of York and southwest- shaly beds, from which Nis-usia festinata was collected1 ward in the broad limestone valley nearly to Thomas- near Bittinger, northwest of Hanover, were described 35 ville. Another large area with few outcrops makes the as Ledger dolomite in earlier reports but are now lowland to the east, south, and southwest of Spring assigned to the Kinzers formation. Grove. North of Hellam Station a narrow lenticular The writers believe the Ledger dolomite is equivalent band of the formation is exposed between the top of to the upper part of the lithologically similar Toms- the Kinzers and the base of the overlapping Conestoga town dolomite of the Chambersburg region in the Ap limestone. palachian Valley. Throughout the valley, dolomite or CHARACTER AND THICKNESS limestone in which fossils are scarce or absent represent The Ledger is everywhere a coarse-grained granular the Kinzers and cannot be distinguished from the en pure dolomite, and is free from silica and other im- closing carbonate formations. The Tonistown dolomite in the Appalachian Valley is overlain by the Lower 32 Stose, G. W., and Jonas, A. L., The southpcistem fades of Lower Cambrian Waynesboro formation which is not present Cambrian dolomite in Wythe & Carroll Counties, Virginia: Virginia Geol. Survey Bull. 51-A, 1938. 33 Resser, C. B., Cambrian system (restricted) of the Southern Appa 85 Stose, G. W., U. S. Geol. Survey Atlas Fairfield and Gettysburg lachians : Geol. Soc. America Special Papers, No. 15, pp. 24-25, 1938. Folio (No. 225), p. 8, 1929; Knopf, E. B., and Jonas, A. I., U. S. Geol. 34 Schuchert, Charles, and Dunbar, C. O., Stratigraphy of western Survey Bull. 799, p. 5-1, 1929 ; Jonas, A. I., and Stose, G. W., Penn Newfoundland: Geol. Soc. America Mem. 1, pp. 18-32, 1934 sylvania Topog. and Geol. Survey Bull. 168, p. 32, 1930. 34 GEOLOGY OP THE HANOVER-YORK DISTRICT, PA. in the Hanover-York Valley. The ILedger dolomite, the Conestoga overlies Ledger dolomite exposed in therefore, is assigned to the Lower Cambrian. small uplifts within the valley; and east of Spring The Vintage dolomite, Kinzers formation, and Ledger Grove it rests also on Ledger dolomite. The Conestoga dolomite are regarded collectively as the equivalent of limestone is not preserved in the valley for several miles the Tomstown dolomite of the Great Valley. These southwest of Spring Grove. On the south side of the three Lower Cambrian formations represent a south Hanover lowland and at Perm Grove, thQ, limestone eastern fossiliferous depositional facies which was de overlies the lower shale member of the Kinzers, but veloped only in the area south of the Welsh Mountain, north of York Road it appears locally to overlap the Chickies, Hellam Hills, and Pigeon Hills anticlines. Vintage dolomite and to overlie the Antietam quartzite, Close folding and overthrusting have brought these In the northern part of the East Prospect syncline, fossil-bearing strata closer to the dolomite facies of the the Conestoga limestone rests on the lower shale mem Great Valley. Fossiliferous facies, similar in lithologic ber of the Kinzers; in the southern part^ it overlaps character and fauna to the Vintage dolomite, Kinzers the Vintage dolomite and rests on the Antietam quartz formation, and Ledger dolomite, are recognized 36 also ite from a point north of East Prospect to east of southeast of Austinville, Va., where they are equivalent Margaretta Furnace, where the formatior is cut off to the Lower Cambrian dolomite (Shady) of the Great by the Cabin Creek overthrust. Small outcrops of Valley and represent different sedimentary facies de residual black slate in the lowland 1 mile so^th of Mar posited on the southeast border of the main Appalachian garetta Furnace may represent the Conestoga lime geosyncline. Later thrust faulting carried this south stone overlying unconformably Vintage dolomite and eastern facies northwestward so that it now rests on Antietam quartzite. the typical Shady dolomite. Three narrow flat-bottomed valleys occur within the Antietam quartzite area on the south sifle of the Mount ORDOVICIAN (?) SYSTEM Pisgah anticline; one south of Delroy, another south CONESTOGA LIMESTONE of Golden along Kreutz Creek, and the third north NAME, DISTRIBUTION, AND UNCONFORMABLE RELATIONS of Ore Valley. No rocks crop out in the ^alleys; but The Conestoga limestone is the only formation of as they are bordered by deposits of brown iron ore and probable Ordovician age present in the area. It was contain limestone soil and small black slate fragments, named from Conestoga Creek in the vicinity of Lan they are believed to be underlain by limestone—pre• caster, where the formation is typically exposed and sumably the Conestoga, because the black calcareous where its unconf ormable relationship to the underlying slate fragments found in the soil are a characteristic formations are well shown. Valleys are generally weathering product of this formation. formed in this limestone, which occupies most of the The Conestoga limestone occupies two narrow valleys broad, flat lowland from York northeastward to in the Jefferson syncline. The northern and longer Wrightsville and underlies the larger part of the city valley extends from Middle Branch of Codorus Creek of York. The outcrop of the formation does not extend southwest to Valley Junction. The limestone overlies to West York nor cross Codorus Creek, for at that lo Antietam quartzite, except north of Smyser Station cality an anticline exposes older limestones which sepa where a small area of Vintage dolomite is exposed rate the formation from another large area of Conestoga between the Conestoga and the Antietam quartzite. limestone extending southwestward from Hoke School The southern valley extends from Smyser Station south- and south of Bair and tapering out 2 miles east of westward to Sinsheim and is separated from the north Spring Grove. Hanover is in the midst of a third large ern valley by an anticline of Antietam quartzite. The area of Conestoga limestone which extends southward trace of the Martic overthrust is the south border of from the foot of the Pigeon Hills nearly to the Stoner the limestone in the southern valley. A long West overthrust. East of Hanover narrow areas of the for Branch is another syncline likewise striking" southwest- mation are exposed in valleys bordered by Harpers ward and probably containing Conestoga limestone phyllite of the Stoner overthrust block. which overlies Antietam quartzite except on the south The Conestoga limestone is unconformable on the side where the Martic overthrust cuts off the formation. underlying formations and therefore transgresses their CHARACTER AND THICKNESS outcrops. Northeast of York, in most places on the north and south sides of York Valley, the Conestoga The Conestoga limestone in the type locality near rests on the Kinzers formation, but it overlies Ledger Lancaster is largely a thin-bedded crystalline blue lime dolomite north of Hellam Station and in the quarries stone with dark argillaceous partings (pi. 7, A). It is north of Wrightsville. (See fig. 8.) South of York generally closely folded, and in many places pro nounced transverse cleavage obscures the bedding. The 86 Stose, G. W., and Jonas, A. I., The southeastern facies of Lower lower part of the formation consists of thick-bedded Cambrian dolomite in Wythe and Carroll Counties, Virginia: Va. Geol. Surv. Bull. 57-A, 1938. granular limestones, with coarse limestone conglomerate PALEOZOIC SEDIMENTARY ROCKS NORTH OF THE MARTIC OVERTHRUST 35 Sericitic clay SE. Approximate uartz SE B FIGDEE 19.—Sections of folded Conestoga limestone in William Grothe Brick Co. clay pit southeast of York: A, Sketch of folds in the limestone showing sericitic clay derived from weathering of highly argillaceous layers ; B, Detail of structure traced from photograph of a fold in the limestone, fold overturned to the northwest, cut by cleavage that dips southeastward and veined by quartz. layers, and in places beds that contain abundant glassy stone in the district are in clay pits of the brick plarts quartz grains and weather to a porous, friable sandstone in the southeastern part of York, where the residual composed of rounded quartz grains. Because the lime clay soil has been stripped from the limestone- over stone is closely folded, its thickness cannot be measured. large areas. In the Win. H. Grothe Brick Co.'s pit, Estimated to be more than 500 feet thick, the formation 1 mile west of Plank Road, the rock is largely thin- is probably much thicker where it is more fully exposed bedded platy blue micaceous limestone with some in the Lancaster and McCalls Ferry quadrangles. thicker granular, crystalline limestone beds as much as The Conestoga limestone in the Hanover-York dis 3 inches thick. The rock contains many wavy micacecns trict is poorly exposed and no continuous section can argillaceous partings and beds as much as 20 feet thick be measured. In the York Valley east of York are composed of calcareous mica schist which weathers to many outcrops of thick-bedded granular limestone. micaceous sandy clay. TKese beds are typical of the Some of these beds contain quartz grains and coarse upper part of the formation. The beds are closely conglomerate and belong to the lower part of the forma folded and the folds are overturned to the northwest tion. Thin-bedded blue limestone is more plentiful and so that all the strata dip southeast. The slaty cleavage represents the upper part of the formation. Thin black is transverse to the bedding and dips 80° SE. The graphitic shale partings within the Conestoga limestone folds were so tightly compressed that the material on have been observed near the south edge of the valley the limbs was squeezed out, so that the beds on the south and east of York and in the adjacent Middletown limbs are thinned and those on the arches are thickened, quadrangle. The best exposures of the Conestoga lime (See fig. 19, and pi. 7, B and C.) 36 GEOLOGY OF THE HANOVE'R-YORK DISTRICT, PA. An abandoned clay pit half a mile to the northwest Kinzers formation (lower member) : Feet and within the built-up part of the city exposes thick Black graphitic slate (upper part contorted)————— 20± Black slate______- 10± beds of gray granular crystalline limestone containing Impure dolomite with slaty partings (may be re scattered glassy quartz grains, thicker beds of conglom worked Vintage with iiiterbedded shale; poorly erate composed of granular limestone pebbles in a fine exposed) ______—_—_—————————————— 2Q± conglomeratic matrix, and interbedded thin layers of blue micaceous limestone. The beds are folded and 50± Vintage dolomite: massive gray granular dolomite. dip 25° to 60° SB., and the well-developed slaty cleav age dips 40° SE. The thick granular and conglomer In the belt of Conestoga limestone southwest of York, atic limestones are typical of the lower part of the in the Hanover quadrangle, outcrops are meager as formation. Similar conglomerates and interbedded the limestone has weathered largely to a deep soil con thin blue limestones crop out in the southern part of the taining abundant small irregular residual fragments of valley east of Spring Plains. At the old Stoner quarry vein quartz. The exposed rock is largely dark-blue north of Stoner Station, in the Middletown quadrangle, impure limestone with some black slate and limestone the following section of the lower beds was observed: conglomerate. In the larger flat valley around Hanover outcrops of the formation are few; and in most places Section of lower part of Conestoga limestone at Stoner quarry the only indications of the formation are the presence north of Stoner Station Feet of small thin residual fragments of black shale, blotched Thick dark granular limestone and fine conglomerate__ 3G=r with white from weathering, and irregular pieces of Thin-bedded dark limestone containing much pyrite___ 2 residual quartz in the soil. The Hershey smd quarry Coarse conglomerate of white and dark granular marble in the northern part of Hanover exposes thick beds of and flat, angular dark slabby limestone pebbles in dark granular quartzose limestone and limestone conglom argillaceous fine conglomerate matrix; merges into dark argillaceous limestone__-______15 erate with a matrix that is composed largely of round Thin-bedded dark argillaceous, micaceous limestone with glassy quartz grains. The conglomerate weathers to shaly partings and pyrite cubes______3 sand. The pebbles of the conglomerate are elongated Massive conglomerate composed of light-colored limestone parallel to the cleavage, which is transverse to the pebbles as much as 2 feet in size, in dark finely con bedding. (See pi. 8, A and B.) These beds are similar glomeratic matrix-______20 to those near the base of the formation which are quarried at Midway and westward in the Gettysburg quadrangle, where the following section was measured: The lower conglomeratic beds are exposed in the south quarry north of Wrightsville, at Susquehanna River, Sections of quartzose limestone of the Conestoga at school in and the section of the exposed beds is given under Kin- North Midway, Smiles west of Hanover zers formation, on page 20, and in figure 8. Feet Blue thin-bedded slaty argillaceous limestone containing A fairly good exposure of the basal part of the scattered pebbles of sandy white marble; veinec1 with Conestoga may be seen along a new road cut on State calcite ______——— 5± Highway 274, from Kline School in the northeastern Sandy limestone; weathers to porous rust-stained sand corner of the York quadrangle to the Susquehanna stone ______-_—___—————— 10 River in the McCalls Ferry quadrangle; but, because Limestone conglomerate containing pebbles of sandy of folding and concealed contacts, thicknesses of beds limestone —___-__———____—_—————————— 5 Banded impure blue limestone_____—_————_—_—— 3 can be only roughly estimated. Dark limestone______-_-__——— 5± White marble containing dark limestone pebbles; long Road section of basal part of Conestoga limestone east of pebbles of sandy limestone at base; local unconformity- 6± Kline School Thick beds of sandy limestone containing many rounded Conestoga limestone: - Feet glassy quartz grains; weathers to crumbly, porous, rust- Blue to gray limestone conglomerate; somewhat stain sandstone (quarried for building sand)_____ 20± folded; beds 10 to 20 feet thick; composed of gray Thin-bedded impure blue limestone (poorly exposed; thick crystalline even-grained limestone pebbles in dark ness not cleterminable). crystalline limestone matrix inclosing rounded glassy quartz grains______40± 54± Concealed fold roadway)______4:)± Thin dense black argillite bed______5± In the Jefferson syncline where outcrops are few, Black limestone conglomerate composed of granular narrow bands of limestone that have been mapped as crystalline limestone pebbles in dark limestone and Conestoga overlie Antietam quartzite. Small masses black slate matrix (exposed in a local anticline be of Vintage dolomite occur at the quartzite contact neath the argillite)______i:0± in places. In the lowland scattered exposures of black 10.1-t clay, probably residue of graphitic limestone, and residual fragments of thin-bedded porous sar dstone and GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 7 B. CLOSELY FOLDED THIN -BEDDED ARGILLACEOUS BANDED CONESTOGA LIMESTONE. In clay pit of William Grolh" Brick Co., southeast of York. Folds overturned to the northwest; layers offset by cleavage dipping 50° SE. A. CONESTOGA LIMESTONE SHOWING CHARACTERISTIC THIN BEDS WITH ARGILLACEOUS AND CARBONACEOUS PARTINGS. Thicker lenticular bed is dolomite. Quarry in eastern part of Columbia. Lancaster quadrangle. C. DETAIL OF STRUCTURE AND CLEAVAGE IN THIN-BEDDED ARGILLACEOUS CONESTOGA LIMESTONE SHOWN IN B. GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 8 A SANDY LIMESTONE AND OVERLYING BED OF SHEARED LIMESTONE CONGLOMERATE B BEDDING SURFACE OF CONGLOMERATE IN SAME QUARRY. OF THE CONESTOGA, HERSHEY SAND CO. PIT, HANOVER. Shows irregular angular blocks of limestone in sandy limestone matrix. Cleavage is steeper than bedding and dips 60° SE. C. UNCONFORMABLE CONTACT OF CONESTOGA LIMESTONE ON LOWER CAM D. FERRUGINOUS LIMESTONE CONGLOMERATE OF THE CONESTOGA LIMESTONE FILLING CREV- BRIAN DOLOMITE, OLD QUARRY 2 MILES NORTHEAST OF LANCASTER. ICES IN LOWER CAMBRIAN DOLOMITE, NEAR CONESTOGA CREEK, 2 MILES NORTHEAST OF Large angular blocks of white marble in basal beds of the Conestoga. LANCASTER. PALEOZOIC SEDIMENTARY ROCKS NORTH OP THE MARTIC OVERTHRTJSI quartz represent the Conestoga. Masses of ferrugi lumbia in the Lancaster quadrangle, and in the Middle- nous chert and brown iron ore lie along the fault on town quadrangle west of Susquehanna River, the writers the south side of the valley. and others have found fossils of Lower Cambrian age At Penn Grove, 4 miles east of Hanover, is a large in similar beds at this stratigraphic position. There limestone cove surrounded by the Harpers phyllite of fore, the mapping of the Kinzers formation and tl 3 the Stoner overthrust block. The only evidence that northern boundary of the Conestoga limestone in those the limestone in the southern part of this cove is areas has been revised. _ (See fig. 24.) Likewise, argil Conestoga is the presence of a few fragments of blue laceous and sandy limestones, originally mapped as limestone partly altered to iron ore, dark ferruginous Conestoga in the Gettysburg area west of the Hanover chert, and much residual quartz. The Conestoga lime quadrangle,39 are beds in the Kinzers formation. TH stone here overlies black slate of the Kinzers formation. revised geology of the adjacent portion of the Gettys burg quadrangle is given in figure 20. UNCONFORMITY AT BASE The irregular distribution and discordance with un AGE AND CORRELATION derlying formations in the region clearly indicate that The Conestoga limestone is unconformable on the the Conestoga limestone is unconformable on these for Ledger dolomite and older rocks of the region and in mations. Because of the general lack of clear contacts, places overlaps tha Antietam quartzite of Lower Cam however, the precise nature of the overlap is difficult to brian age. These facts indicate that the Conestoga determine. In general, the dip of the Conestoga lime limestone was deposited after a period of uplift and stone beds accords with the dip of the underlying or erosion and that it is therefore considerably young0!!' adjacent formation; but in a few quarries the relations than the underlying formations. In the Hanover- are clearly discordant. In the old quarry north of the York-Lancaster area, the Ledger dolomite of Lower Lancaster water works (pi. 8, C], a conglomerate, com Cambrian age is the youngest rock overlain by the posed of large blocks of white marble in a darker finely Conestoga limestone. In Chester Valley near Coates- conglomeratic limestone matrix, at the base of the ville, limestones continuous with and tentatively corre Conestoga, rests with marked unconformity on the lated with the Conestoga limestone overlie Elbrook Lower Cambrian dolomite. South of this quarry, deep limestone, and west of Coatesville these rocks progrers- channels and narrow crevices, with nearly vertical walls ively overlap the older formations down to txie and as much as 20 feet deep, in the underlying limestone Antietam.40 are filled with this limestone conglomerate. (See pi. No fossils have been found in the Conestoga limestone 8,/>.) in this area. As stated previously, fossils collected by West of the quarry in which the unconformity is ex the writers in the quarry of the York Valley Lime & posed is another quarry operated by C. D. Stoner of Stone Co., 5 miles east of York, were originally re Columbia.37 The present opening on the north side of ported " to be of Chazyan age. They are now knovm the quarry exposes a gentle anticline in thick-bedded to be of Lower Cambrian age and the beds in which ribbed blue limestone and thinner argillaceous beds. they occur are part of the Kinzers formation. At Hen- When this quarry was visited in connection with the derson Station in the eastern part of Chester Valley preparation of the report on the Lancaster quadrangle, south of Norristown, limestones tentatively correlated the writers believed that the ribbed and rhythmically with the Conestoga have yielded the only determinable banded earthy limestones belonged in the Conestoga fossils that may belong to this formation. E. O. Ulrioh formation because east of York similar beds at the same and A. F. Foerste have assigned Beekmantown age to stratigraphic position contain fossils which were then these cephalopods and gastropods.42 The limestores considered to be of probable Chazyan age. As the in Chester Valley are therefore of Lower Ordovician brachiopod is now known to be NLm&ia festinata (Bill age. The age of the Conestoga limestone in the type ings),38 the banded blue limestone in which it occurs locality in Lancaster Valley and Westward in the Han is of Lower Cambrian age and undoubtedly part of the over-York district can be ascertained only if fossils sre underlying Kinzers formation. In the south side of the obtained in that region. Consequently, at present the quarry, the southward-dipping blue crystalline lime formation is classed as of probable Ordovician age. stone and limestone conglomerate of the Conestoga overlie the Kinzers formation in an unconformable or 39 Stose, G. W., U. S. Geol. Survey Geol. Atlas (no. 225), Fairfleld- Gettysburg folio, Gettysburg geologic map, 1929. fault relation. North of Lancaster westward to Co- 40 Stose, G. W., U. S. Geol. Survey Geol. Atlas (no. 223), Coatesville- West Chester folio, Coatesville geologic map, 1932. ST Stose, G. W., and Jonas, A. I., Geology and mineral resources of 41 Stose, G. W., and Jonas, A. I., Geology and mineral resources of the Lancaster quadrangle, Pa.: Pennsylvania Geol. Survey, 4th ser., the Middletown quadrangle, Pa.: U. S. Geol. Survey Bull. 840, p. 35, Topog. and Geol. Atlas No. 168, p. 75, 1930. 1933. 38 Stose, G. W., and Jonas, A. I., Age reclassiflcation of the Frederick 43 Jonas, A. I., and Stose, G. W., Age reclassiflcation of the Frederick Valley (Maryland) limestones: Bull. Geol. Soc. Amer., vol. 27, p. 1671, Valley (Maryland) limestone: Geol. Soc. America Bull., vol. 47, pp. 1936. 1670-1673, 1936. 38 GEOLOGY OF THE HANOVEK-YORK DISTRICT, PA. In the southwestern end of the Hanover Valley at largely derived from argillaceous and arenaceous sedi the Pennsylvania State line the Conestoga limestone mentary rocks, and include mica schist, qua.rtzite, the is in strike with the limestones of the Frederick Valley, Wakefield marble, and associated volcanic flows and Md., 15 miles to the southwest. The intervening area inetomorphosed tuffs. is covered by Triassic rocks. The limestones of Fred The albite-chlorite schist facies of the Wissahickon erick Valley comprise the Frederick limestone with formation occupies the southeastern part of the block. fossils of Upper Cambrian age and the overlying Grove In the northwestern part of the albite-chlorite schist limestone which contains Lower Ordovician fossils. area, a belt containing infolded metabasalt extends The Frederick limestone is a thin-bedded argillaceous from a point southwest of Brownton southwestward limestone with limestone conglomerate beds, and the across the area and passes into Maryland. Northwest Grove limestone is purer limestone with dolomitic beds of the Wissahickon formation and the metabasalt belt •Gh Heilam conglomerate member _, FIGUBB 20.—Geologic map of eastern part of the Gettysburg quadrangle, re vised to accord with present mapping ia the Hanover quadrangle. Sandy limestone, previously mapped as part of Conestoga limestone, and white marble formerly mapped as Ledger dolomite, are now regarded as Kinzers. containing glassy quartz grains near the base. The are fine-grained albite-chlorite schist and chloritoid Conestoga is more closely folded and more metamor schist, here called the Marburg schist. The Marburg phosed than the limestones of Frederick Valley, but it schist contains infolds of associated quartzi*es in the bears a strong lithologic resemblance to them and may Yoe and Wentz synclines. be equivalent in part to both the Frederick and Grove WAKEFIELD MARBLE limestones, and possibly in part, Upper Cambrian in DISTRIBUTION age. The Wakefield marble is apparently the oldest forma BOCKS OF THE MABTIC OVEBTHBUST BLOCK tion in the region and underlies the albite-chlcrite schist The Martic overthrust block lies southeast of the facies of the Wissahickon formation. In a narrow known Paleozoic rocks of the East Prospect and Jeffer valley in the southern part of the district, els y derived son synclines and the Holtz anticline. The rocks of from weathered marble extends southwestward from the Martic overthrust block are crystalline schists, Hokes post office to Blackrock at the Maryland State ROCKS OF THfi MARTIC OVE'RTHRUST BLOCK 39 line. South of Blackrock and at a point 1 mile east of associated volcanic rocks. The correlation is not well Lineboro, other narrow valleys in Maryland contain established; therefore, the name Wakefield is used here. beds of marble, which extend into Pennsylvania. The In the valley east of Loganville blue thin-bedc^d marble is poorly exposed in Pennsylvania, but south- crystalline limestone contains argillaceous bands which westward in Maryland it crops out across Carroll and form slaty muscovite partings. This rock resembles the Frederick Counties,43 where it is associated with Silver Bun limestone,45 of Maryland, which in places volcanic rocks. seems to grade into the Wakefield marble and may be In the valley east of Zumbrum school 2 miles south equivalent to it. In this report the blue limestone is of Marburg, white impure 'marble is exposed in an included with the Wakefield marble. old quarry east of the road along the valley. The mar ble is surrounded by the Marburg schist and is exposed METABASALT along a fault that offsets the quartzite associated with The metabasalt occurs in narrow areas surrounc>.d the schist. Twelve miles to the northeast in a valley, by the albite-chlorite schist facies of the Wissahickon which extends from a point three-quarters of a mile formation from points near Brownton and Brogueville east of Loganville northeastward to East Branch of Station southwestward to the Maryland line. The long Codorus Creek, blue crystalline limestone is in strike narrow areas in the northeast part of the belt wicMn with white marble. The limestone crops out in several to 6 miles in the vicinity of Glen Rock. The best ex old quarries on the northwest side of the valley. At posures are several narrow bands in the valley of Co both ends of the area are limonite pits, now abandoned dorus Creek and in road and railroad cuts from G^n and filled with water. The limestone is surrounded by Rock southeastward to Shrewsbury Station, but fresh Marburg schist; both formations are closely folded; exposures are few. Because it is less resistant to erosion and at the southwestern end, a narrow infold of the than the inclosing Wissahickon formation, the metals- schist extends into the limestone. salt occupies narrow longitudinal valleys between ridges of albite-chlorite schist and chloritoid schist. The CHARACTER AND THICKNESS metabasalt weathers readily to rusty porous blocks No fresh exposures of the Wakefield marble have been ("worm-eaten rock") which the farmers use exten found in the district. Everywhere the rock is weathered sively in making stone walls. to a blue clay. In Carroll County, Md., the marble In the district the metabasalt is a green schistose rock of this belt is a crystalline bluish-gray to white composed of albite, uralitic hornblende, and epidote. It marble composed of coarsely crystalline calcite with contains veins of quartz and epidote, and, in the more some finer grains of calcite, quartz, and muscovite. massive outcrops, has amygdules of quartz and epidcte. Under the microscope, the calcite is seen to contain in Thin sections under the microscope show albite, zoistte, clusions of quartz and feldspar; and impure layers of and epidote, which are secondary to a lime-soda feldspar, the marble contain muscovite, biotite, and chlorite. and uralite and chlorite derived from pyroxene. The The accessory minerals are leucoxene, pyrite, zircon, and metabasalt is closely folded; and the crests of the foTds tourmaline. Where the metabasalt is absent between are sheared out in large part, forming foliation layers the marble and the albite-chlorite schist facies of the which generally dip 45° NW. This foliation 46 is cut Wissahickon formation, the marble grades upward into by a transverse nearly vertical cleavage. Metabasalt the Wissahickon schist through a calcareous schist which is infolded with the overlying albite-chlorite schist of contains bands of muscovite, chlorite, albite, quartz, and the Wissahickon, which it resembles in weathered crit- calcite. Its thickness in southern Pennsylvania and the crops, and with chloritoid schist, which may be of fpf- adjacent part of Maryland can not be measured but is faceous origin but which has been mapped with the estimated to be 100 feet. aMte-chlorite schist facies of the Wissahickon for mation. NAME AND CORRELATION WISSAHICKON FORMATION The Wakefield marble takes its name ** from Wake- NAME AND DISTRIBUTION field Valley in western Carroll County, Md. It has been correlated with the Cockeysville marble of The Wissahickon formation was'named from Wis^a- Baltimore County, Md. The Cockeysville marble is hickon Creek near Philadelphia, where the rock is an coarser grained and is overlain by the oligoclase-mica oligoclase-biotite-muscovite schist. This schist lies on schist facies of the Wissahickon formation, but has no the southeast side of the Peters Creek quartzite. On the northwest side of this quartzite there is a belt of albite- 48 Jonas, A. I., and Stose, G. W., Geologic map of Frederick County and adjacent parts of Washington and Carroll Counties, Md., Maryland 46 Jonas, A. I., and Stose, G. W., New formation names used on the Geological Survey, 1938. geologic map. or Frederick County, Md.: Wash. Acad. Sci., vol. 28, ** Jonas, A. I., and Stose, G. W., New formation names used on the p. 346, 1938. geological map of Frederick County, Maryland, Washington Acad. Sci. 46 For definitions of these terms, as used in this report, see p. 41, Jour., vol. 28, p. 346,1&38. under Wissahickon formation. 40 GEOLOGY OP THE HANOVEfo-TORK DISTRICT, PA. chlorite-muscovite schist regarded as a different meta- folded with them. Because of close folding, various morphic facies of the Wissahickon formation. This kinds of schist and quartzite of the Wissahickon forma schist has been called the albite-chlorite schist facies of tion may occur in the same outcrop; consecuently, the the Wissahickon formation. This albite-chlorite schist varieties of schists are not indicated on the map. facies occupies most of the southeastern part of the Quartzite is mapped south of Felton in th°> valley of Hanover-York district. The northwest boundary of the Muddy Creek where the rock is infolded T^ith albite- exposures extends from a point about a mile north of chlorite schist. Similar quartzite exposurer have been Hockey southwestward through Springvale, Graydon, traced from a point near Springvale southwestward, and Glenville. The Wissahickon formation lies south passing north of Glen Rock; others lie northwest of east of the Marburg schist and contains infolds of meta- Sticks. Quartzite has been mapped also on the north basalt. The best outcrops are in valleys that cut across west side of two metabasalt belts between Seitzland the strike of the formation, namely, those of North and and Shrewsbury Station. The quartzite is fine-grained, South Branches of Muddy Creek and Deer Creek, which with a white or green color. It has muscovite partings. flow southeast, and those of East and South Branches Some layers contain stretched blue or milky quartz of Codorus Creek, which flow northwest across the pebbles which, in the area north of Glen Rock Valley, Hanover quadrangle. are as much as two inches long. The quartzite is in The belt of albite-chlorite schist is the southwestern folded with green quartzose chlorite schist and lustrous continuation of the albite-chlorite schist belt of the blue chloritoid schist with crumpled quartzose layers. McCalls Ferry quadrangle.47 From the York-Hanover North of the wide area of metabasalt at Glen Rock, district it extends southwest into the albite-chlorite the quartzite containing blue quartz layers is infolded Wissahickon formation occurring in Baltimore County, with chlorite schist, albite-chlorite schist, and meta Md.48 basalt. The quartzite north of Rockey and in strike with CHARACTER outcrops at Springvale has a white sugary texture, con tains muscovite partings, and is closely folded. It re The Wissahickon formation in the Hanover-York dis sembles the quartzite that occurs northeast of Sticks trict is a coarse-grained sparkling grayish-blue or green and south of Glenville and that extends southwestward schist, whose dominant minerals are albite, chlorite, toward Blackrock. As these quartzites are erposed only muscovite, and quartz. It is interlayered with quartz- in stream valleys, contact boundaries are shown by ite and muscovite and chloritoid schists. In general dashed lines. the schists are of coarse grain in the southeast part of STRUCTURE the area and become finer grained to the northwest. Before describing the schists of the Wissahickon for The metamorphism is that of the "green-schist facies." mation in microscopic detail, a general account of the The schists in the Wissahickon formation may be structure of the area is essential. The axis of the Tuc- divided into a type containing albite and a type contain quan anticline, which is in the albite-chlorite schist ing chloritoid and lacking albite. The size of the albite facies, crosses the southeast corner of the 7rdrk quad grains differs greatly in the albitic schist, which may rangle and extends to the edge of the district in a line be separated into two varieties. One is a muscovite- nearly parallel to South Branch of Muddy Creek. This chlorite-quartz schist characterized by small albite fold is the southwestward continuation of. the Mine grains. It is garnetiferous in part of the area, and Ridge anticline, in which pre-Cambrian gneisses and has a microscopic layering of fine opaque dust, largely overlying lower Paleozoic sedimentary rocks are exposed ilmenite and iron-oxide particles, which forms a stream in the Quarryville B. THIN SECTION OF SPECIMEN SHOWN IN A, SIMILARLY ORIENTED. A. POLISHED SURFACE OF RECUMBENT FOLD IN CHLORITE-MUSCOVITE-QUARTZ SCHIST TUCQUAN ANTICLINE. Muscovite with layers of fine dust (m); chlorite (c); muscovite porphyroblast (mp) lying across earlier-formed muscovite. X 8%. Looking S. 65° W. Axial plane horizontal; cleavage dips 60° NW. Natural size. C. POLISHED SURFACE OF RECUMBENT FOLD IN CIILORITOID SCHIST, 6 MILES NORTH WEST OF TUCQLAN ANTICLINE. D. THIN SECTION OF SPECIMEN SHOWN IN C. Looking N. 65° E. General foliation dips 35° NW.; transverse cleavage dips 70° SE. Natural size. Muscovite, chlorite, and cbloritoid blades (m); quartzite layers (q). X GEOLOGICAL SURVEY r PROFESSIONAL PAPER 204 PLATE 10 •».-. if. A. POLISHED SURFACE OF RECUMBENT FOLD IN ALBITE-CHLORITE-MUS- B. THIN SECTION OF SPECIMEN SHOWN IN A. COVITE-QUARTZ SCHIST, 7 MILES NORTHWEST OF TUCQUAN ANTICLINE. Recumbent fold in part transformed to foliation. X 6. Looking S. 35° W. General foliation dips 45° NW. Limbs partly sheared out. Natural size. C. MUSCOVITE-CHLORITE-QUARTZ SCHIST FROM MUDDY CREEK FORKS, 1 MILE SOUTH D. ALBITE-MUSCOVITE-CHLORITE SCHIST FROM FENMORE WEST OF HIGH ROCK, McCALLS FERRY QUADRANGLE. X 6. Shows contorted muscovite and chlorite containing layers of ilmenite and iron oxide dust (i), which pass Contains ilmenite (black specks). Cleavage dipping 70° SE. is prominent in micaceous layers. through the albite grains (a), and muscovite porphyroblast (m) diagonal to layering. ROOKiS OF THE MARTIC OVEKTHRUST BLOCK 41 cline in the McCalls Ferry quadrangle, for a distance of southeast of Laurel on North Branch of Muddy Creek 5 miles. on the crest of the Tucquan anticline where the axie of Even where folds are invisible to the unaided eye, the fold and the foliation are horizontal. The thin thin sections generally show closely appressed folds section (pi. 9, B) shows muscovite and chlorite, which whose axial planes are parallel to the foliation of the are flexed on the outside of the fold and include layers schist. In such rocks the larger folds have been sheared of a fine, opaque dust, probably ilmenite and oxide of out along the crests, and the microscopic crumples are iron.50 The coarser-grained ilmenite, titanite, and the only remnants of the recumbent structure. Folia micaceous minerals are bent on the crest. On the con tion, therefore, is here used to denote a mechanical cave side of the arch, the micas are mechanically undis- differentiation of original material into more or less torted; and their crystallization outlasted the flexing of irregular layers, the layering being the result of the fold. Hence, in respect to the mica crystallization, slipping in closely appressed and drawn out folds so the folding is paracrystalline. Coarse blades of mus that the crests of the individual folds are largely de covite and chlorite, formed late in the process of crys stroyed. Such a foliation lying parallel to transposed tallization, lie at angles to the direction of the .earlier- xS'-planes has been called by E. B. Knopf *9 "transposi formed micas and are arranged in two intersecting tion cleavage," in contrast to "slaty cleavage" or trans groups of parallel lines. verse cleavage which cuts across the xS'-planes. A schist of similar composition (pi. 10, C] from At the crest of the Tucquan anticline, the foliation is Muddy Creek Forks, one mile southwest of High Eock horizontal or gently rolling. The axial planes of the in the McCalls Ferry quadrangle, shows folded quartz recumbent folds, which are parallel to the foliation, are lenses and well-developed later cleavage. This rock also horizontal at the crest of the arch; and both the contains also coarse crystals and fine grains of ilmenite. axial planes and the foliation dip northwestward on the A recumbent fold in a schist of different composition is northwest limb of the arch and southeastward on the shown in plate 9, C. The specimen was collected 6 miles southeast limb. The_ dip of the foliation layers and northwest of the Tucquan anticline, 2 miles southwes^ of of the axial planes of the folds gradually steepens in Felton, where the foliation dips 35° NW. The fold both directions away from the crest of the Tucquan shows crumpling and displacement along slip planes, arch. At Brownton, 7 miles northwest of the crest of which dip steeply southeast. The schist (pi. 9, D) ex the anticline, the foliation dips 55° NW., is minutely hibits paracrystalline folding of muscovite, chlorite, and folded and crumpled, and is broken by steeply-dipping chloritoid, which in part were formed late in the fold superimposed cleavage transverse to the micaceous ing. This chloritoid schist is infolded with albite- layers and more prominent in them. chlorite schist. Plate 10, A and B illustrates a bluish-gray muscovite- MICROSCOPIC DESCRIPTION chlorite schist collected a short distance to the southv^est of the place where the specimen shown on plate 9, C and Polished specimens of schist with recumbent folds, D was obtained. The recumbent folds are partly in some of which the crests are in part or entirely sheared out and are recognizable only in the quartrose sheared out into foliatiqnj layers, together with layers. The specimen shows paracrystalline folding thin sections cut from these specimens, are given in and late coarse unbent blades of chlorite and muscovite. plates 9 to 11. They illustrate the development of Ilmenite, which is present as fine opaque dust and thin transposition cleavage or foliation formed by the shear plates, has been folded. In both specimens (pis. 9, C ing out of the crests of the recumbent folds. All the and 10, A), the paracrystalline micaceous minerals of polished specimens and thin sections figured in this the schist are lustrous and not sparkling because the report were cut at right angles to the fold axes, or mica flakes were shearing out during folding. lineation of the Tucquan anticline. In this area the fold In a fine-grained albite-chlorite-muscovite schist from axes are horizontal or have a maximum pitch of 20°- Fenmore (see pi. 10, Z>), prominent layers are formed 40° SW. As the lineation on the cleavage planes is by muscovite and opaque dust of ilmenite and iron parallel to the fold axes, the sections are cut at right oxide. The albite porphyroblasts in the rock contain angles to the lineation where fold axes are not evident. streamlines of the opaque dust and mica of the ground- The polished specimens are marked to show their orien mass; and the centers, which contain the helicitic pat tation in the field outcrops, and the thin sections exhibit tern, are surrounded by clear albite rims formed rt a on a minute scale the megascopic structure seen in the later time. This rock shows a crumpled, thin-layered outcrops. foliation in which recumbent folding is discernible only Plate 9, A shows a recumbent fold in a specimen of in minute folds. The larger flexures were sheared out mica schist collected north of High Rock and 2 miles 50 The microscopic and chemical determination of the ilmenite and 48 Knopf, B. B., Retrogressive metamorphism and phyllonitization : iron oxide, which occurs in the fine opaque dust, was made by J. J. Glass, Am. Jour. Sci., 5th ser., vol. 2, pp. 16-18, 1931. J. J. Fahey and T. Stadnichenko. 462857—44———4 * 42 GEOLOGY OF THE HANOVER-YORK DISTRICT, PA. along the crests, and the resultant foliation layers were no sense a stratigraphic succession. Durirg the rise folded later in the movement which slightly rotated the of the Mine Ridge anticline, the foliation, formed as a albite grains and developed a steep superimposed result of the slipping movement that accompanied re cleavage transverse to the foliation. cumbent folding, has been folded into the Tucquan The thin section shown in plate 11, A is cut from a anticline and its minor folds. No estimate of thickness, sparkling inuscovite-chlorite schist collected 1 mile south therefore, can be made and no vertical section of the of Springvale. Foliation planes dipping 50° NW. and formation can be given. The metamorphirm, origin, a steeper intersecting cleavage are the only structures correlation, and age of the Wissahickon formation will visible in the outcrop. The thin section shows lenses be discussed after the description of the Marbirg schist. of folded muscovite and chlorite alternating with MARBURG SCHIST quartzose layers. This chlorite and muscovite is para- crystalline to the shearing out of folds. Coarse musco NAME AND DISTRIBUTION vite porphyroblasts of later generation are not bent by The Marburg schist 51 was named from Marburg, the cleavage that intersects the older muscovite. Large York County, Pa., a village 5 miles southeast of Han black rods of ilmenite are partly surrounded by bor over. The Marburg schist in a belt about 5 miles wide ders of chlorite. The coarsely crystalline muscovite of crosses the Hanover-York district along the northwest the second generation spangles the rock and tends to ern border of the Martic overthrust block. The forma obscure the presence of early deformed muscovite and tion enters the area from the McCalls Ferry auadrangle chlorite. where it is well exposed along Susquehanna Pwer from The coarse-grained albite-chlorite schist (pi. 11, B) a point south of Creswell Station to and beyond Star is made up of chlorite, muscovite, epidote, apatite, Rock. In the report on that area,52 schists nc w mapped titanite, and ilmenite in layers between the more quartz-' as Marburg were included with the albite-chlorite schist ose bands. The micaceous layers contain coarse, some facies of the Wissahickon formation; and, because of what rounded albite metacrysts in which are stream their quartzose character, certain schists near Long lined inclusions of such minerals as garnet, epidote, Level, York County, and south of Creswell Station, muscovite, and ilmenite. Sedimentary grains of apa Lancaster County, were mapped as Peters Creek quartz tite are greatly crushed, and the ilmenite plates are ite. In the present consideration of the Hanover-York bent. Folding of the schist was paracrystalline. The district the Marburg schist has been separate! from the pattern of the inclusions in the albite metacrysts re Wissahickon formation, which lies southeast, because it cords an early folding. These inclusions are not in line is finer grained and, in the southwestern part of the with the mica and chlorite blades that lie parallel to area, contains schistose rocks apparently derived from the folded layers of the schist; hence the writer con volcanic tuff. The line separating the two formations cludes that the albites were rotated somewhat during is dashed on the map because grain size and met amor- the folding, subsequent to their crystallization. phism decrease gradually from southeast to northwest. The graphitic quartzite (pi. 11, G) came from one of The associated quartzites in the upper part of the Mar the quartzose layers in a graphitic schist, which is well burg schist are exposed in the Yoe and Wentz synclines. exposed on the highway 1 mile south of Seitzland, where CHARACTER it is in contact with metabasalt. Recumbent folding is visible in the quartzose layers, which contain fine musco The Marburg schist is chiefly bluish-gray to silvery- vite blades. The schistose layers, composed of fine green fine-grained schist which contains eitl °,r musco grained muscovite and graphite, are broken by trans vite, chlorite, albite, and quartz, or muscovite, chlorite, verse cleavage dipping 80° SE. chloritoid, and quartz. Northeast of the Erst Branch of Codorus Creek in the York quadrangle, the schist THICKNESS is coarser grained and sparkles with porphyroblasts of The Wissahickon formation includes schists of vary muscovite. Because the varieties of schist that con ing composition, crystallinity, and degree of meta- stitute the Marburg schist are interfolded and, in gen morphism. Their most prominent structural feature is eral, are separable only by examination in thin section, the foliation resulting from closely packed recumbent they are not separated on the map. Beds of quartzite folds in which the closures usually are sheared out and and conglomerate form the upper part of the formation. the limbs torn apart by slipping movements. If the In the sparkling muscovite schist of the northeastern layered structure in the recumbent folds was original part of the area (pi. 12, A) the felty crumpled layers of bedding layers, the foliation developed by shearing out fine muscovite, chlorite, and albite and the quartzose of the folds is also largely parallel to the original bed 01 Jonas, A. I., and Stose, G. W., New formation nanieR used on the ding. The layers, whether they were originally sedi geologic map of Frederick County, Maryland. Washington Acad. Sci. mentary beds or not, are completely transposed and in Jour., vol. 28, pp. 346-347,1938. ™ Knopf, B. B., and Jonas, A. I., Geology of the McCalls Perry-Quarry- verted so that the present superposition of layers is in ville district, Pa.: TJ. S. Geol. Surv. Bull. 799, pp. 25-37, 1929. ROCKS OF TEE MARTIC OVE'RTHRUST BLOCK 4.3 bands are crossed by a well-developed cleavage, which ridges on which Dallastown and Bed Lion are built. A dips 85° SE. Another specimen of Marburg schist (pi. conglomeratic facies of the quartzite forms Huntrick, 12, B) contains coarse ilmenite porphyroblasts and Beecher, and Saubel Hills, which range in altitude from coarse blades of muscovite that lie in two intersecting 900 to 1,000 feet. groups of parallel flakes at angles of 45° to the cleavage. The quartzites and slates in the Yoe syncline lie These muscovite porphyroblasts for the most part were northeast of Inners Creek and Rye and are surrounded not bent by the cleavage; and their crystallization, by the Marburg schist. From Red Lion northeastward therefore, was later than the earlier generation of mus small areas of the quartzite lie south of the main syncline. covite and chlorite forming the foliation layers and The quartzites in the Wentz syncline, named from a later than the shearing movement that formed the village in Maryland 1 mile south of West Manheim, cleavage. extend from a point near Loganville southwestward to In the Hanover quadrangle the muscovite and chlorite the Maryland State line, a distance of 12 miles. At porphyroblasts, where present, are fine-grained and are its broadest point, north of Hokes post office, tr -UH 2i.—Sections of Marburg schist and associated quartzites at Brodbeck : A, Sketch in railroad cut showing conglomerate beds in quartzite and the interpreted structure. B, Detail of struc ture in quartzite at north end of section. Bedding planes, emphasized by quartz stringers, are closely folded, and pebbles are elongated parallel to cleavage which dips steeply northward. C, Detail of cleavage observed in quartzose layers; steep dip in hard 0-inch layers : dip 30° N. to nearly horizontal in softer 2-inch beds. land-derived quartz grains, but the evidence for tuff a - erate and phyllite is estimated to be about 150 feet. The ceous origin is not conclusive. section (see fig. 21) is complicated by folding, and the The quartzites in the Wentz syneline are made up exposures are too shallow and discontinuous for the largely of dark-green ferruginous, sericitic quartzite structure to be completely determined. The sequence interbedded with blue and green slate, some beds of has been interpreted as follows: which contain blue or milky quartz grains, muscovite, and chlorite. A coarse, pebbly green conglomerate in Composite section of the quartsitcs at the top of the Murburr/ layers 2 to 4 feet thick is interbedded witli the dark schist at Brodbeck Feet quartzite and blue slate. The schistose conglomerate Sheared conglomerate containing pebbles up to 3 inches contains flattened lenticular pebbles of quartz and in size, and hard white granular quartzite (conglom serieite; and the blue and milky quartz pebbles are erate member)______25± elongated, some being as much as 3 inches in length. Green ferruginous quartzite and quartz cellist; contains Muscovite and chlorite are developed in the partings. glassy quartz grains in lower part______50± Thick-bedded white to ferruginous quartzite cor^aining The weathered conglomerate is porous and rusty brown, blue quartz grains and small pebbles; weathers porous owing to the leaching out of its ferruginous cement. and rust spotted______25± Conglomerate and interbedded quartzite is well ex Gray phyllite______20± posed on a curve of State Highway No. 616,1 mile south Thick-bedded granular white quartzite containing blue west of Larue. The beds are closely folded—the axes of quartz grains with shiny shale partings; in part ferru ginous ; weathers banded, porous, and rust spotted ; inter the folds striking N. 40° E. and dipping 20° NE—and bedded gray slate in lower parf______30± are cut by transverse cleavage which dips 80° NTV. Dis placement to the southwest, occurred along cross shear planes which dip 30° NE. The quartz conglomerate Green phyllite or platy slate, rust spotted from pyrite layers contain pebbles 1 inch long and are interbedded (Marburg schist). with rusty, green quartzite. The conglomerate crops METAMORPHISM OF THE SCHISTS OP THE MARTIC out to the north and to the south of infolded green AND STONER OVERTHRUST BLOCKS quartzite and phyllite. The thick beds of conglomerate DESCRIPTION are the most conspicuous part of the quartzite series and, The Wissahickon formation in Maryland, in the vicin in general, are the only beds traceable on the uplands. ity of the anticlines of Baltimore gneiss, is a coarse In stream valleys, as at Brodbeck, the pebbly quartzites grained schist of mesozone type. It contains biotite, may be seen in outcrop. muscovite, oligoclase, quartz, garnet, staurolite, and The best outcrops of the quartzites associated with kyanite. Staurolite and garnet porphyroblasts, which Marburg schist in the Wentz syneline are along Codorus grew during the folding, contain quartz inclusions that Creek north of Brodbeck, where for three-fourths of a represent available silica in excess of that needed for mile the rock is almost continuously exposed. There, the growing crystals. Coarse blades of biotite and mus the thickness of the quartzite and interbedded conglom covite formed during the last stage of ci^stallization. ROCKS OF THE M'ARTIC OVE'RTHRUST BLOCK 45 Absence of deformation shows that their growth out a mile of Felton. A garnetiferous chlorite-muscovite- lasted the folding, or, in other words, was post-tectonic. albite schist (see pi. 15, A and 5), collected from the The terms "epizone" and "mesozone" used by Griiben- crest of the Tucquan anticline on the Susquehanna mann and Niggli 53 place an emphasis - on the depth River, shows a crumpled foliation, formed by a shear jfactor in metamorphism. Eskola 54 however, uses the ing out of the earlier recumbent structure that is pre terms "green schist" facies and "amphibolite schist" served elsewhere in the area. The garnet in this ro"k facies to designate, respectively, metamorphism of lower has not been altered to chlorite, although the other con and higher rank without implication as to the depth. stituents of the rock—chlorite, muscovite, and albite— He defines a metamorphic facies as a group of rocks are of the "green schist" facies of metamorphism. At characterized by a definite set of minerals, which, under localities in the York quadrangle, the garnets have the conditions of temperature and pressure that obtained altered to chlorite on their surfaces and in cracks, during their formation, were in perfect equilibrium with thereby indicating a retrogression in metamorphis^n. each other. The minerals in the oligoclase-mica schist Porphyroblasts of magnetite and tournialine occur in facies of the Wissahickon formation in Maryland be many places in the Wissahickon formation. long to the amphibolite schist facies and the rocks show Except for the presence of garnet in certain layers, little evidence of a change in metamorphic conditions the Wissahickon formation and the metabasalt flows in throughout crystallization. the southeastern part of the Hanover-York district con On the northwestern border of the belt of oligoclase- form to the "green schist" facies of metamorphisTi, mica schist, evidence of a change in metamorphic and show a coarse crystallization of albite, quartz, mus intensity during folding is shown by retrogression of covite, and chlorite. The metabasalt contains also earlier-formed garnet and biotite to chlorite, and of uralitic hornblende. Like the garnets, the coarse albite staurolite to muscovite before metamorphism ceased. metacrysts in the albite-chlorite schist of the Wissa These diaphthoritic .schists in the area southwest of hickon formation are postcrystalline in respect to the Oxford, Pa., were described in the report of the McCalls streamline of inclusions (see pi. 10, Z>), but are para- Ferry-Quarryville district.55 They extend southwest- crystalline to the mica and chlorite crystallization. A ward into Maryland across Cecil and Harford Counties border of clear albite around some of the cores with into Baltimore County, where they lie on the northwest helicitic inclusions indicates a renewal of crystallization side of the Phoenix anticline and southeast of the Peach during late stages of folding. The mica flakes and al Bottom syncline. It is evident in that area that the bite grains are paracrystalline with the recumbent fold minerals of higher rank formed in earlier stages of ing. Crystallization continued during the shearing cut crystallization were no longer stable under the condi of these folds and the formation of foliation layers. tions of temperature and pressure that obtained in the The transverse cleavage is the latest structure and tends later stages. to shear out the earlier formed mica layers. Crystalli In the Peach Bottom syncline lying northwest of this zation continued even after the development of this retrogressive zone, the Peters Creek quartzite also has cleavage, for coarse porphyroblastic muscovite, chlorite, undergone retrogression in the partial alteration of bio and chloritoid (see pis. 11, A and 12, B) are not dis tite to chlorite. The schist of the Peters Creek quartzite turbed by the transverse cleavage. is finer grained than the oliogoclase-mica schist facies of The albite-chlorite schist of the northwestern part of the Wissahickon formation to the southeast; is a the Wissahickon area is finer grained schist of the "gre?n crystalline rock containing chlorite with biotite relics, schist" facies. The foliation is more closely folded, the epidote, quartz, and albite; and lies in the Peach Bottom dips are steeper, and the transverse cleavage is better syncline southeast of the albite-chlorite schist facies of developed. This zone, as well as that to the southeast, the Wissahickon formation. This facies of the Wissa contains ilmenite in weU-«rystallized rods and thin hickon occupies a wide area in northern Baltimore laminae, which in many places, are included in chlorite County and extends northwestward into the Hanover- and clinochlore porphyroblasts. It is possible that these York district. In northern Baltimore County the minerals may have been derived from earlier minerals of albite-chlorite schist contains biotite and garnet, in part higher rank, either biotite or staurolite, although no altered to chlorite. Biotite has not been found in the relics of these minerals have been found. albite-chlorite schist in the Hanover-York area, but The Marburg schist, which lies northwest of the firer garnet persists as porphyroblasts and inclusions in the grained albite-chlorite schist of the northwestern port albite and has been observed northwestward to within of the area of the Wissahickon formation, is of still fir te schist Singewald 71 also interprets the crumpled streamlines from Peters Creek, Pa. The albite porphyroblasts in of inclusions in the albite porphyroblasts of the Balti these rocks contain inclusions of muscovite whose direc more County area as relict minerals, but doubts that the tion he calls "albite trends," and he says that the albite angular discordance with the groundmass is due to rota trends are not relict structures but are controlled by the tion during folding. lattice of the feldspar grains. His second conclusion is Knopf 72 stated that in crystalline schists, "a valuable that the albite trends "are indirectly related to the pres criterion of the relation between deformation and crys ent fabric of the rock, in that the cleavages controlling tallization is given by porphyroblasts filled with inclu the trends have been developed in the zone of the S- sions." To illustrate, she describes a biotite schist from planes of the rock"; or, in other words, the inclusions Connecticut which contains streamlines of black dust in grew along the cleavage planes that were parallel to the the matrix and in the biotite, and in which "the biotite axis of folding. He ascribes the formation of the mus porphyroblasts are displaced with respect to the matrix, covite inclusions to "late hydrothermal solutions per indicating that movement has been renewed to the extent meating the plagioclase along the planes of greatest of displacing the already quietly formed host." An ex accessibility." ample of porphyroblastic growth during crystallization The evidence presented by Ingerson seems to justify and differential displacement is shown in plate 15, A and these conclusions for the rocks he described, but the B. The rock is a muscovite-chlorite schist from Tuc- writer questions the regional application of the term, raian, Pa. The specimen and the thin section \vere cut "similar trends," as it is used in another one of Inger- normal to the regional lineation and parallel to the son's conclusions: "Since there are similar trends in the direction of the slip. In the garnet porphyroblasts the plagioclase porphyroblasts in all of the rocks of Ordo- schistosity, outlined by black dust lines, is shaped in vician age and older in this region, their presence cannot spiral curves. These curves indicate that the garnet be used as a criterion of age relations." rolled during its growth. A similar rotated garnet por- Because of the evidence given previously, the writer phyroblast is described by Miigge 73 and is reviewed by believes that albite porphyroblasts were formed at Gilluly.74 The rolling recorded in the garnet and the several stages during deformation. In some places the slipping along the planes of the "foliation in the schist inclusions are relict structures, and in others the albite have a geological significance that is called to our atten grains were rotated during later folding. Rocks in tion by Gilluly in this review where he states that "Al which the porphyroblasts contain minerals of higher though the recorded translation in each schist plane may metamorphic rank than those of the matrir are cited be small, when these differential motions are-integrated to support the argument against the conclusion that through a thick packet of schist planes, the total dis all inclusions in albite grains were formed by late hy placement of the top of the formation with respect to its drothermal solutions; for if this were so, the hydro- base may well amount to many times the thickness of thermal solutions should have formed minerals in the the schist measured normal to the schistosity—hence groundmass similar to those included in the albite meta in this sense a schist may represent a distributed crysts. Petrofabric studies of the type made by Inger overthrust." son are helpful in elucidating the metamorphic history 71 Singewald, J. T., Jr.: Weathering and albitization of the Wissahickon of crystalline schists, but similar studies accompanied schist of Prettyboy dam, Baltimore County, Maryland : Geol. Soc. Amer. by detailed field work over a much wider area should be Bull., vol. 43, pp. 457-460, 1932. 72 Knopf, B. B., and Ingerson, E. : Structural Petrology, Geol. Soc. carried on before generalizations can be made as to the America Mem. 6, p. 109 and pi. 13, figs. 2-8, 1938. 73 Miigge, O., Bewegungen von porphyvoblastics -in phylliten und ihre 75 Cloos, Ernst, The application of recent structural m?thods in the messung. Neues Jahrb. fiir Min. Geol. und Pal., Beilage-Band 61. Abt. interpretation of the crystalline 'rocks of Maryland, Maryland Geol. A. pp. 409, 1930. Survey, vol. 13, pp. 88-92 and pi. 9, fig. 1, 1937. 71 Gilluly, James, Report of the committee on structural petrology, 76 Ingerson, Earl, Albite trends in some rocks of the Piedmont: Am, Nat, Research Council, pp. 52-57, 1938, Jour. Sci., 5th ser., vol. 35-A, pp. 127-141,1938. GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 11 A. MUSCOVJTE-CHLORITE SCHIST 1 MILE SOUTH OF SPRINGVALE. B. COARSE-GRAINED ALBITE-CHLORITE-MUSCOVITE SCHIST, 1 MILE SOUTH OF ANSTINE. Quartzose lenses (q); coarse muscovite porphyroblasts (m); ilmenite fi). X 6V4- Shows paracrystalline folding. Coarse albite metacrysts (a). Foliation dips 20° NW. Crossed nicols. X 8y2. C. GRAPHITIC QUARTZITE, 1 MILE SOUTH OF SEITZLAND. Shows recumbent fold (f) whose axial plane dips 40° NW., and transverse cleavage that dips 80° SE. X 6. GEOLOGICAL SURVE" PROFESSIONAL PAPER 201 PLATE 12 A. MARBURG SCHIST. THREE-QUARTERS OF A MILE NORTH B. MARBURG SCHIST, 1 MILE NORTH OF WINDSOR. OF CRALEY. Chlorite-albite-quartz schist showing transverse cleavage dipping 80° SE. Muscovite-chlorite-albite-quartz schist with quartzose (lighter) layers. Ilmenite (block prisms) and muscovite porphyroblasts (light-colored laths) Cleavage dips 85° SE. X 6. are not bent by the cleavage. X 9. C. MARBURG SCHIST, FROM MARBURG. Muscovite-chlorite scbist with quartzose layer (white). Section from arch of a close fold, showing transverse cleavage dipping 80° SE. X 27. GEOLOGICAL StJRVEY PROFESSIONAL PAPER 204 PLATE 13 B. MARBURG SCHIST, SHOWING GREATER DETAIL IN PART OF THIN SECTION ILLUS A. MARBURG SCHIST, 1 MILE NORTH OF MARBURG. TRATED IN A. X 27. Fine-grained muscovite-chlorite-quartz schist, showing close folding and "transposition" cleavage. Transverse cleavage dips 80° SE. Field in rectangle enlarged in B. X 9. C. QUARTZITE ASSOCIATED WITH MARBURG SCHTST, iy2 MILES SOUTHEAST OF DALLASTOWN. Contains blue quartz grains (q) and aggregates (a) that are composed of subangular quartz in fine black dust. Cleavage in slate band (dark) dips 75° NW. X 6y2. GEOLOGICAL SURVEY lSflfiii'*''PROFESSIONAL PAPER 204 lPLATE1l !14 A. CHLORITOID-MUSCOVITE-QUARTZ SCHIST FROM SAUBEL B. CHLORITOID-MUSCOVITE-QUARTZ SCHIST FROM HILL. HOFFACKER VALLEY. Chloritoid shows as dark prisms arranged in sheaves. Cleavage dips 80° Chloritoid sho\vs as dark fibers. X 27. NW. X 27. I C. BANDED CHLORITE-MUSCOVITE-QUARTZ SCHIST, HALF A MILE SOUTH OF FREYSVILLE. Dark prisms are ilmenite. Transverse cleavage dips 80° NW. X f>l/2- ROCKS (XF THE MARTIC OVE'RTHRUST BLOCK. metamorphism and the tectonic history of the Glenarm age. These relationships indicate that this pegmatite 'series and the adjoining Paleozoic rocks. is later than the folding of the schist and may be re In the work on the McCalls Ferry-Quarryville dis lated to the Triassic diabase of the Safe Harbor dilre trict, the writers 77 pointed out two major problems, rather than to an, older (Paleozoic) igneous intrusion namely, the variability of metamorphism in the rocks associated with the regional metamorphism. of the Glenarm series, and the localization of high Intrusive rocks are widespread in the schists of tl 3 metamorphic intensity in the area around Mine Ridge Glenarm series in Maryland and Pennsylvania southeast and southwestward. Much of the summary of conclu of the Hanover-York district and the Mine Ridge arei. sions given in that report (see pp. 139-140) is reaffirmed The granitic intrusives are the Sykesville granite and here. Port Deposit granite. As stated on page 48 of this re This abnormal relation of strong metamorphic intensity in the port, both Ingerson and the writer believe that these Paleozoic rocks with lower intensity in the pre-Cambrian thrust granitic bodies were intruded before the regional meta block suggests that the dominant metamorphism in both Pale morphism. The hydrothermal emanations genetically ozoic and Glenarm strata was subsequent to the overthrust. related to these granites may have had some influence This idea is confirmed by the character of the thrust plane in the metamorphism of the schists of the Glenarm se so far as observation of it has been possible. The thrusting appears to have taken place under conditions that were favor ries ; but it is more probable that thermal effects of a able to molecular rearrangement and metamorphism. younger granite, not visible at the surface in Pennsyl The strong degree of metamorphic intensity localized in the vania, produced the strong metamorphism and the late autochthonous Paleozoic beds near the surface emergence of porphyroblastic crystallization in the rocks of the Mine the fault plane suggests that the increased load produced by Ridge belt and the region to the southwest. the weight of the thrust block may have had some influence in the metamorphism. But the conditions for crystalloblastic SUMMARY alteration could hardly have been produced by depth of burial alone. The normal load of sediments upon the Conestoga forma Heat and pressure, produced during folding, hav°> tion at the time of metamorphism could hardly have amounted metamorphosed the rocks of the Martic overthrust block to as much as 10,000 feet. Even if this normal load were con siderably increased by the weight of the thrust block the addi with a general decrease in intensity from southeast to tional load could not have been sufficient to cause anything northwest. Folding and metamorphism took place over but a cataclastic metamorphism in the autochthonous Paleozoic a long period. Metamorphic intensity has been re sediments or in the displaced thrust block. versed in certain zones, the earlier metamorphism being The only feasible explanation for a folding and metamorphism of higher rank than the later. Metamorphism was con of the thrust block that would inhibit or obliterate the effects of cataclastic metamorphism is a rise of geothermal gradient. temporaneous with the folding, and outlasted it, as A localized rise of geothermal gradient suggests the influence of shown by porphyroblasts in large part undisturbed by highly heated underlying igneous rock, and such thermal in the latest structure—the transverse cleavage—which fluence combined with the locally increased load of the faulted tended to shear out the earlier-formed minerals. rock would doubtless account for the peculiar concentration This latest metamorphism, which reached its maxi of intense metamorphism in the overridden Paleozoic rocks. The hypothesis is alluring, but has been insusceptible of proof except mum intensity to the east in the McCalls Ferry-Quarry insofar as the extensive tourmalinization and pegmatitization ville district, has produced a coarser crystallization of of the Paleozoic rocks indicate the passage of magmatic emana the schists in the eastern part of the York area tlum tions from an underlying igneous intrusion. southwestward along the strike, and has affected also Pegmatite veins have penetrated only into the Lower the Harpers phyllite and Antietam quartzite in tH Cambrian Hellam conglomerate member of the Chickies Cabin Creek and Stoner overthrust blocks, which lie quartzite on the south flank of Mine Kidge. More re north west \of the Martic overthrust block. Metamor cently pegmatite has been observed near Safe Harbor, phic intensity wanes rapidly northwest of the Stoner Pa. In a quarry opened during the construction of the overthrust in the Hanover-York Valley and in tl ^ dam and power plant of the Safe Harbor Water Power Pigeon and Hellam anticlines northwest of the valley. Co., a Triassic diabase dike cuts Antietam quartzite and In these anticlines the Harpers phyllite, which is the the overlying Vintage dolomite; and at the contact with best index of metamorphism of the rocks of that area, is diabase the dolomite is baked and contains knots of a fine-grained rock. The Vintage dolomite shows d°- epidote. A pegmatitic differentiate of the-diabase ex velopment of muscovite in its schistose beds; and the posed in the quarry contains coarse pink feldspar. Conestoga limestone, where most closely folded norMi North of Safe Harbor in the cuts of the Pennsylvania of the Stoner overthrust, contains muscovite in the ar Railroad, albite-biotite schist of the albite-chlorite gillaceous layers. schist facies of the Wissahickon formation contains QRIGIN OF THE WISSAHICKON FORMATION, MARBURG similar pegmatite veins, which cut across the foliation SCHIST, AND ASSOCIATED QUARTZITBS of the schist, and are inclined to the plane of the cleav- The Wissahickon formation in the Hanover-York « Knopf, E. B., and Jonas, A. I., op. cit., pp. 118-141, 1929, district has been described as made up of three types of 50 GEOLOGY OF THE HANOVE'R-YORK DISTRICT, PA. schist with infolded quartzites: (1) albite-chlorite-mus- sent tuffaceous layers in that formation. The opaque covite schist containing1 layers of opaque dust, (2) al- dust layers and rods, largely ilmenite and iron oxide, bite-chlorite-muscovite schist containing coarse albite found in part of the Wissahickon formation, are original metacrysts in which epidote occurs as inclusions in the constituents of the rock. Likewise, certain tuffaceous albite and in the groundmass, and (3) chlorite-muscovite phyllites in Maryland contain the layered opaque dust schist containing chloritoid. These mineral differences and the crystalline form of ilmenite. This fact suggests are due to original differences in composition. Albite that the schists of the Wissahickon formatior that have and chloritoid do not occur together, for chloritoid is a high content of titanium and iron oxide may be of produced in rocks that contain abundant alumina and volcanic origin. relatively scant magnesia, potassa, and lime. The albitic The Marburg schist which lies northwest of the Wissa Hoosac schist and the chloritoid Rowe schist,78 of west hickon formation is less metamorphosed and finer ern Massachusetts and Vermont, also record in the min grained than the Wissahickon formation. Th°- Marburg erals of their crystallization a similar original difference resembles the Wissahickon formation in containing in composition. Like the types of schist in the Hanover- chloritoid schist, albite-chlorite schist, and chlorite- York region, these rocks in the Taconic quadrangle are muscovite schist with opaque dust layers. Southwest infolded and cannot be mapped separately. in Maryland, similar fine-grained chloritoid schists or Chloritoid schists occur also in the Marburg schist phyllites and chlorite-muscovite schist layered with which, southwestward along the strike in Carroll and fine opaque dust, in part ilmenite, have tuffaceous char Frederick Counties,79 Md., show evidence of tuffaceous acteristics. These schists, however, may be the finer origin. There, blue, purple, and green schists or phyl- grained equivalent of the albite-chlorite schist, facies of lites containing chloritoid, or chlorite, and muscovite, in the Wissahickon formation. The rhyolitic flows and part show tuffaceous structure and are interlayered tuffaceous phyllites in Maryland are interbedded with witli aporhyolite, metabasalt flows, and tuffs. In the red and purple arkosic quartzite, sericitic quartzite, Hanover-York district, a tuffaceous character is not blue and purple phyllite with siliceous Ir.yers, and evident in the Marburg schist. South of the Jefferson coarser conglomeratic quartzite that contains grains and syncline, the blue, purple, and green phyllitic schists pebbles of blue quartz, feldspar grains, and angular of the Marburg are closely similar in appearance and green argillaceous1 fragments. These quartzites are be composition to the tuffaceous phyllites of Maryland; lieved to be stream-worked tuffs mixed with detrital and the Marburg schist may be in part of pyroclastic quartz and appear to be a part of the volcanic series. origin. Gilluly 81 describes a similar mixing of clastic and pyro Because chloritoid is a highly aluminous mineral, it clastic material in the Burnt River schist and Elkhorn has been regarded, like staurolite, as indicative of meta Ridge argillite of Oregon. morphosed sedimentary rocks. However, bentonite,80 The quartzites in the Wentz syncline, especially the which is altered volcanic ash or tuff, is also high in alu conglomeratic variety, resemble conglomerates, which mina. Bentonite is composed largely of clay minerals are regarded as in part tuffaceous, farther southwest in formed by the alteration and devitrification of glassy Maryland. The conglomerate layers of the quartzite volcanic tuff, much of which contains detrital material. contain flattened pebbles of fine sericite and quartz in If the chloritoid schists in this area were derived from which the subangular quartz grains (see pi. 13, G) sug volcanic material which had undergone such chemical gest a volcanic origin. changes before metamorphism, a volcanic origin for Although it is more intensely metamorphosed, the these chloritoid schists should not be inconsistent. conglomeratic quartzite in the Wissahickon formation, In Maryland tuffaceous phyllites, in strike with the south of Felton and of Grraydon, resembles the quartzite Marburg schist of the Hanover-York district, lie north associated with the Marburg schist. The mrscovite in the matrix is coarser and the argillaceous pebbles are west of the marble-volcanic belt that extends through Maryland northeastward into the Hanover-York dis sheared out in the direction of the cleavage. This con trict. In the York area the Wissahickon formation sur glomeratic quartzite may be equivalent to the quartzite rounds the northeast end of the metabasalt and grades associated with the Marburg schist. northwest into the Marburg schist. The chloritoid AGE AND RELATIONS OF THE BOCKS OF THE MABTIC schists of the Wissahickon formation also may repre OVEBTHBTJST BLOCK ss Prindle, L. M., and Knopf, E. B., The geology of the Taconic quad The rocks of the Martic overthrust block belong to the rangle : Amer. Jour. Sci., 5th ser., vol. 24, pp. 288-289, 1932. 79 Jonas, A. I., and Stose, G. W., Geologic map of Frederick County Glenarm series, and the northwestern part of the block and adjacent parts of Washington and Carroll Counties, Maryland: is included in the Hanover-York district. The Glenarm Maryland Geol. Survey, 1938. 80 Ross, C. S., Altered Paleozoic volcanic materials and their recogni tion : Am. Assoc. Petroleum Geologists Bull,, vol. 12, pp. 146-149, 164. 81 Gilluly, James, Geology and Mineral Resources of the Baker quad 1928. rangle. Oregon : U. S. Geol. Survey BnlJ. 879, p. 12, 1937, ROCKS OF THE MARTIC OVE'RTHRUST BLOCK 51 series is composed of crystalline schists, which lie south AGE OF THE ROCKS OF THE GLENARM SERIES east of the Paleozoic limestones and dolomites of the In a preliminary paper on the marble-volcanic area Hanover-York Valley and the underlying arenaceous of Carroll and Frederick Counties, Md.,82 the quartzites Lower Cambrian rocks. The Paleozoic limestones and of the Sugarloaf syncliue were regarded as Lower Cam dolomites form the synclinal valleys in the vicinity of brian, and their occurrence in synclines of the marble- York, Hanover, Lancaster, Quarryville, and the Chester volcanic series was cited as proof of the pre-Cambrian Valley and the Great Valley northwest of the Triassic age of the Glenarm series, of which the marble-volcanic rocks. series is a part. Later work in the area has led the The points of difference between the schists of the writer to regard the lower beds of these quartzites as Glenarm series in the Martic overthrust block and the a part of the volcanic series and as equivalent in pp,rt Paleozoic rocks to the northwest are: The schists of to similar quartzites associated with the Marburg schist the Martic overthrust block are dominantly of argil in the Hanover-York district. laceous and arenaceous facies, whereas the Paleozoic In Sugarloaf Mountain, Md., tliick white pure quartz rocks are largely limestones and dolomites with arena ites overlie ferruginous quartzites that are iiiterbedded ceous beds in the lower part. As far is as known, the with slates and arenaceous rocks, which are probably rocks of the Glenarm series contain no fossils. The tuffaceous in part. The uppermost beds of white Paleozoic rocks are fossiliferous. In the Hanover-York quartzite cap the highest peak of the mountain, and district and southwest in Maryland, volcanic flows and lower quartzite beds form the crest of the mountain tuffs make up a large part of the Glenarm series; and north of the peak and of Furnace Ridge. These quar^z- in the area farther southeast, intrusive rocks are wide ites have been called Lower Cambrian since the days of spread. In contrast, no Paleozoic effusive or intrusive J. P. Lesley and G. H. Williams (1892), but no fossils rocks occur except for basalt flows and diabase dikes have been found in them. As their Cambrian age has found near Jonestown, Pa., and scanty pegmatite in the not been proved, this evidence for the pre-Cambrian age basal Cambrian near Mine Ridge. The metamorphism of the Glenarm series has little weight. of the rocks of the Glenarm series continued over a long In Virginia two areas of fossiliferous slate of Cincin- period and was intimately connected with the folding. natian age are infolded with the schists of the Glenarm The latter part of their metamorphic history was shared series along the axis of the Peach Bottom syncline. The by the Paleozoic rocks to the northwest, especially in the Quantico slate lies along the border of the Coastal Plain vicinity of the Mine Ridge anticline. 18 miles southwest of the District of Columbia at Poto- Along the contact between the schists of the Glenarm mac River. At the western side the slate overlies green series and the Paleozoic rocks from Schuykill River stone schist and granite gneiss. On the east these slates south westward to the Maryland line in the southwestern are overlapped by sedimentary formations of the Coastal part of the Hanover quadrangle, the schists of the Glen Plain. The Arvonia slate lies in north-central Virgir ia arm series overlie Harpers phyllite, Antietam quartzite, farther to the southwest. The basal conglomerate of and Vintage dolomite of Lower Cambrian age, and the slate imconformably overlies the Columbia granite Conestoga limestone of Ordovician (?) age. On the and the Peters Creek quartzite which the granite east side of Frederick Valley, Md., the schists of the intrudes. Rock similar to the Columbia granite extends Glenarm series overlie Lower Cambrian Antietam in discontinuous areas northeastward to the Potomac quartzite and Upper Cambrian Frederick limestone. River, where it passes into the Sykesville granite of The contact of the Glenarm series on Paleozoic rocks, Maryland between the mouths of Rock Creek and Rock therefore, is not conformable. Evidence given in the Run on the Potomac River. In Virginia, therefore, the chapter on the structure of the district shows that the Columbia granite and the Peters Creek quartzite, whi^h schists of the Glenarm series were probably thrown into is a part of the Glenarm series, are pre-Cincinnatirn, recumbent folds during the movement which brought that is, pre-Eden. The Peters Creek quartzite is con them forward to lie on the Paleozoic rocks. This re siderably older than Cincinnatian, as is shown by the cumbent folding was an earlier phase of the deforma fact that it was intruded by granite, uplifted, and eroded tion that arched and folded the Paleozoic rocks and the before the Arvonia slate was deposited. Therefore, the underlying pre-Cambrian rocks together with the over upper part of the Glenarm series, that is, the Peters lying crystalline schists of the Glenarm series. The Creek quartzite and Wissahickon formation, cannot be direction of the fold axes in the schists of the Glenarm equivalent to the Martinsburg shale, as has been sug series conforms with that of the underlying Paleozoic gested,83 because the Martinsburg shale, whose basal rocks and, therefore, offers no evidence to prove either ^Jonas, A. I., Pre-Cambrian rocks of the western .Piedmont of Mary land : Geol. Soc. America Bull., vol. 35, pp. 361, 363, 1924. that the rocks of the Glenarm series were moved to tlieir ^Mackiu, J. H, The problem of the Martic overthrust and the age present position by overthrusting or that they were of the Glenarm series in southeastern Pennsylvania : Jour. Geology, vol. 43, p. 358, 1935. Miller, B. L., Age of the schists of South Valley Hills, originally deposited where they now occur. Pa.: Geol. Soc. America Bull., vol. 46, p. 754, 1935. 52 GEOLOGY OF THE HANOVER-YORK DISTRICT, PA. beds are of Trenton age, is largely Eden in age and be later in the Coatesville-West Chester Folio 91 expressed longs in the lower part of the Cincinnatian series. the belief that a belt of schist half a mile or more wide The Cardiff conglomerate and the Peach Bottom slate on the south side of Chester Valley is of Ordovician age of Maryland and Pennsylvania were included in the but that the Wissahickon formation to the southeast of Glenarm series and designated as pre-Cambrian ** in this narow belt is pre-Cambrian. Mackin,92 like Haw 1923 by the Federal Survey and Maryland Geological kins, is of the opinion that the Glenarm series is Paleo Survey because the writers of the paper cited were unable zoic rather than pre-Cambrian in age, and that the Wis to find any evidence of unconformity at the base of the sahickon formation is the metamorphosed equivalent of Cardiff conglomerate. Further, although Lesley 85 re the Martinsburg shale. One of his reasons for this ported that specimens of Buthotrephis flewuosa were view is that volcanic rocks of post-Beekmantown age at found in the Peach Bottom slates, the specimens cannot Jonestown, Pa., overlie Beekmantown limestone and be located, and no other fossils have been obtained from underlie the Martinsburg shale, just as the volcanics of the area. the Glenarm series overlie the Wakefield marMe. The In a recent report on York County, Pa.,86 which in proof that the Peters Creek quartzite and hence the cludes part of the Peach Bottom syncline, Stose and Wissahickon schist are not of Martinsburg age was Jonas give their reasons for concluding that the Cardiff given above. The presence of volcanic rocks in both conglomerate and Peach Bottom slate are probably of series seems to the writer to be a coincidence and not Ordovician age and are not part of the Glenarm series. evidence of equivalent age upon which to basa- a corre As bedding folds are plainly visible in some of the slate lation. quarries, obviously, the folding of the Peach'Bottom Mackin concludes also that the steep contac* of lime slate has not destroyed the bedding. The Peach Bottom stone and schist south of Chester Valley is a normal slate occurs in the same syncline with the Quantico and contact because the South Valley hills are parallel in Arvoiiia slates,' which contain fossils of Ordovician a TEIASSIC SYSTEM NEWARK GROUP GENERAL DESCRIPTION The Newark group comprises a wide belt of red sandy FIGURE 22.—Ideal progressive sections across the Triassic basin in the rocks that extend from New Jersey south westward across Fairfield-Gettysburg, Pa., area, illustrating mode of deposition of Pennsylvania and Maryland into Virginia. This belt, sediments as floor of basin subsided during progressive sinking and down-faulting, and resulting northwesterly dips of beds. €Ols, which has a maximum width of about 30 miles at the Cambrian and Ordovician limestones ; -Cq, Cambrian quartzite ; ve, pre- Delaware Kiver, is 10 miles wide in the vicinity of the Cambrian volcanic rocks. Hanover quadrangle. It covers the northwest third of the quadrangle and extends farther northwestward for part of the basin but later spread progressively farther about 3 miles into the Carlisle quadrangle. The rocks west as the basin was deepened by the gradual sinking are mostly red, but beds of light-gray sandstone and of the floor on the west side. Only a part of the total greenish to light-yellow arkosic sandstone are common thickness of the strata, therefore, will be found at any in the lower part. one place. The postulated mode of deposition is illus In the Hanover quadrangle the average dip of these trated in figure 22. red rocks is 30° NW., though the dip ranges locally from Two formations of the Newark group are distin guished in the Hanover quadrangle—the lov^er, called 8 Jonas, A. I., Tectonic studies in the crystalline schists of southeastern the New Oxford formation, composed of red sandstone, Pennsylvania and Maryland: Ani. Jour. Sei., 5th ser., vol. 34, pp. 383-384, 1937. shale, and many light-gray interbedded arkosic sand- T'RIASISIC SYSTEM 55 stones; and the upper formation, called the Gettysburg erate, two of which have been mapped, are stratigraphi- shale, composed almost wholly of red shale and soft red cally slightly higher. The abrupt hill made by one of sandstone. these beds of conglomerate is very noticeable on the higl - NEW OXFORD FORMATION way (U. S. 30) at Farmers. A prominent bed of con glomerate half a mile north of La Bott has been traced NAME AND DISTRIBUTION eastward 3 miles to a point where other conglomerate The New Oxford formation was named from New beds come in at a still higher stratigraphic level. This Oxford, Adams County, where the Triassic formations distribution of conglomerate shows that the shore cur in southern Pennsylvania were first studied in detail and rent moved northeastward. their thickness determined. The formation occupies a The top of the New Oxford formation is placed wher«j belt about 5 miles wide in the northwest third of the beds of light-gray arkosic sandstone end or become Hanover quadrangle. Owing to the greater resistance scarce and red shale predominates. This boundary is of the gently dipping Triassic sandstone and conglom more or less arbitrarily mapped and probably is not erate in comparison with the adjacent Paleozoic lime exactly the same horizon in the sedimentary sequence in stones and shales, the southeast edge of the belt is for this district as it is in the type area to the southwest the most part sharply marked by a low escarpment. Assuming that beds are not duplicated by strike fault That the reel beds once extended somewhat farther south ing, the thickness of the formation as determined from east is shown by small remnants of red calcareous sand width of outcrop and dip of beds in the Hanover quad stone preserved in pockets in the limestone in quarries rangle is about 6,000 feet. northwest of York, 1 mile southeast of the present edge of the Triassic area. This sandstone contains marble UNCONFORMITY AT THE BASE pebbles. South of Abbottstown the Triassic rocks lap The New Oxford formation rests unconformably on onto the slope of the Pigeon Hills. Northeastward, the the* Paleozoic rocks that in large part constitute its floor. southeast edge of the New Oxford formation passes just In the northeastern part of the Hanover quadrangle, th e north of La Bott and Thomasville, and thence bends New Oxford overlaps the end of a belt of Kinzers formr- more northeasterly to the northeast corner of the Han tion and at the northeast corner lies on Vintage dolomite. over quadrangle. Its northwest edge is marked approx Southwestward, it lies chiefly on Ledger dolomite but imately by the winding course of Conewago Creek. overlaps the Kinzers at several places. Northwest of West York, a small erosional remnant of Triassic sand CHABAOTEB AND THICKNESS stone is preserved on a hill of shale of the Kinzers for The New Oxford formation consists of red to purplish- mation. To the southwest, the New Oxford formation red sandstone and shale but is characterized by many overlies Ledger dolomite nearly as far as ThomasviLb intercalated beds of light-gray or greenish-yellow ar- where the two formations strike almost at right angles kosic sandstone. Most of the arkosic beds are crumbly to each other. West of Thomasville the Triassic 'rocks sandstone containing many grains of white kaolinized overlap the shale of the Kinzers formation, which there detrital feldspar, glassy quartz, and sparkling flakes of strikes at right angle to the contact; and farther west detrital light-colored mica. Some of the beds contain they lie on Vintage dolomite. On the flanks of th°< small rounded quartz pebbles and weather to sand and Pigeon Hills the New Oxford formation rests on th^ gravel.. Interbedded with the arkosic layers are red Cambrian quartzites and the pre-Cambrian metabasalt. shale and soft red micaceous sandstone, which underlie small valleys between ridges and spurs of the harder AGE AND CORRELATION arkosic sandstone and produce alternate red and yellow Few fossils have been found in the Newark group, and streaks in the soil and along country roads. those that are known are of continental type that corre In the vicinity of the Pigeon Hills, a conglomerate sponds to the terrestrial character of the red sediments. at the base of the formation is composed chiefly of round B'ragments of silicified wood have been found in plowed white quartz pebbles in a red sand matrix. (See pi. 15, fields north of this area in the vicinity of Elizabeth - O.} This conglomerate is coarsest and thickest south town, Bainbridge, and York Haven. These were iden of Abbottstown, at the widest part of the Pigeon Hills, tified by Wherry 9 as Ar NAME AND DISTRIBUTION AGE AND CORRELATION The Gettysburg shale is named from Gettysburg, Where conglomerates or pebbly sandstone do not Adams County, where it is typically exposed. In the occur, the general soft shaly character typical of the Hanover quadrangle the shale is present only in the formation persists in this area. Small fossil shells northwest corner, northwest of East Berlin, Dars School, identified as Estheria ovcnta. Lea, a phyllopod crustacean, and Davidsburg. Its outcrop in the quadrangle is were collected by the writers from a green shale in the about 3 miles wide. In the extreme northwest corner, Gettysburg shale at Middletown. The sarr^ form has the shale is intruded by a thick diabase sill, which is been found in black shale at the base of the Few Oxford about 1 mile wide in outcrop. The sill is part of the formation near Farmers and to the southwest and Gettysburg sill described in the Fairfield-Gettysburg northeast at several other places in Pennsylvania. folio 10 and the report on York County, Pa.,11 and Dinosaur foot prints have been found 13 in red sand extends northeast and southwest for many miles. stone of the Gettysburg shale in this region, and reptile and fish remains have been collected from equivalent CHARACTER AND THICKNESS beds farther east in Pennsylvania. The formation is of The Gettysburg shale in the type area consists chiefly Upper Triassic age. It is lithologically similar to the of soft red shale and some soft red micaceous sandstone. Brunswick shale, the upper formation of the Newark In the Hanover quadrangle, conglomerate beds occtir in group in the eastern part of the State; and the two the midst of the red shale. To the north in the New formations are approximately equivalent. Cumberland quadrangle, these coarser strata thicken and are composed of massive hard sandstone and lentic TBIASSIC IGNEOUS BOCKS ular beds of conglomerate that make the Conewago Hills DIABASE and, therefore, are named the Conewago conglomerate GENERAL DESCRIPTION member. These resistant beds make a low ridge, Airy Hill, which crosses the northwest corner of the Hanover The rocks of the Hanover-York district p,re intruded quadrangle and is the southwest extension of the by diabase, chiefly in the form of narrow dikes. Conewago Hills. In places the dikes make low, linear ridges strewn with The red shale adjacent to the diabase sill in the north residual rounded rusty tough boulders loyally called west corner was altered when the diabase was intruded "iron stones." A thick sill of diabase intrudes the red and was hardened by the heat of the molten mass into Gettysburg shale and follows the strike of the beds in a dense, tough purplish-black porcelanite containing ir a northeastward direction across the northwest corner regular knots of green epidote. The diabase and baked of Hie Hanover quadrangle. The sill dips 40° NW. shale are harder than the unaltered red rocks and con parallel with the bedding of the enclosing red shale. sequently make a line of broad, low hills. Northwest 13 Stose, G. W., Glauberite crystal cavities in the Triairsic rocks in the of Yorkhaven, 12 miles north of this area, garnet crys- vicinity of Gettysburg, Pa.: Am. Minerologist, vol. 4, No. 1, pp. 1-4, 1919. J0 Stose, G. W., U. S. Geol. Survey, Fairfleld-Gettysburg folio, Geol. 13 Hickok, W. O., and Willard, Bradford, Dinosaur foot tracks near Atlas (No. 225), pp. 11-13, 1929. Yocumtown, York County, Pa.: Pennsylvania Acad. Sci. Proc., vol. 7, u Stose, Geo. W., and Jonas, A. I., Geology and mineral resources of pp. 55-58, 1933. Cleaves, A. B., Quarry gives up dinosaur footprints York County, Pa.: Pa. Topog. and Geol. Survey, 4th ser., Bull. C 67, pp. after millions of years; Pennsylvania Dept. Int. Aff. Monthly Bull., vol. 4, 120-124, 1939. No. 3, pp. 12-15, Aug. 1937, and No. 4, pp. 8-11, Sept. 1937. GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 15 N. 20 W. A. FOLIATION LAYERS IN GARNETIFEROUS CHLORITE-MUSCOVITE SCHIST, TUCQUAN, PA. B. GARNETIFEROUS CHLORITE ML SCOVITE SCHIST. Recumbent folds sheared out. Natural size. Thin section of specimen shown in A. S-shaped lines of black dust in garnet indicate rotation during growth. X 15. V C. QUARTZ PEBBLE IN CONGLOMERATE NEAR BASE OF NEW OXFORD FORMATION NORTH- D. GARNET (ANDRADITE) CRYSTALS IN SOLUTION POCKETS IN METAMORPHOSED WEST OF LA BOTTE. CONGLOMERATE IN THE GETTYSBURG SHALE, NEW CUMBERLAND QUADRANGLE, Cut through and glickensided by fault plane. Natural size. 15 MILES NORTHWEST OF YORK. Natural size. GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 16 PHILADELPHIA^^ SKETCH MAP OF TRIASSIC SEDIMENTARY ROCKS IN WESTERN NEW JERSEY, PENNSYLVANIA, AND MARYLAND, SHOWING DIABASE SILLS, CROSS- CUTTING BODIES, AND DIKES. Dotted areas, Triassic sedimentary rocks; solid black areas and heavy black lines, Triassic diabase; and lighter black lines, faults. The Gettysburg sill crosses the northwest corner of the Hanover quadrangle. Hanover-York district shown by rectangle. (Face p. 57) TRIASSIC IGNEOUS ROCKS 57 At its contact with the sill the shale was baked to a dike extends an equal length before it, and the enclosing hard grayish-blue rock by the heat and hot water that crystalline rocks, are covered by sediments of the Coastal escaped from the injected mass. As both the diabase Plain. and the baked shale are more resistant to erosion than SILLS the adjacent unaltered red shale, they form a low ridge. The diabase sills, with which many of the dikes con DIKES nect at their northwestern ends, coalesce to form exten sive intrusive bodies in the northwestern part of the Several diabase dikes cross the Hanover-York district. Triassic area of Pennsylvania. (See pi. 16.) The larger The trend of these dikes is for the most part a little sills are the Haycock, Ziegler, Saint Peters, Yorkhaven, west of south. The Stonybrook dike enters the area and Gettysburg. They parallel the strike of the sedi from the north, crosses the York quadrangle with several mentary rocks for long distances, and then the intrusive breaks and offsets, passes through Seitzland, and ex body cuts across the strike at right angles. Most of these tends into Maryland. It makes a conspicuous ridge crosscutting bodies extend to the northwestern edge of strewn with diabase boulders where it cuts the Conestoga the Triassic basin where they terminate against the limestone. Where it is well exposed in a cut along the faults that form the boundary of the basin. Each of Pennsylvania Railroad north of Stonybrook the dike these intrusive bodies, therefore, has the form of a great is vertical and about 50 feet wide and cuts sharply across tilted trough bounded on the southeast side by the west- limestone beds that dip 30° SE. It is paralleled on dipping sills and at the ends by the cross-cutting bodies the west by five thinner, less extensive dikes that cut and open at the west. The large intrusive bodies of both the Triassic sedimentary rocks and the older crys diabase lie almost entirely outside of the Hanover-York talline rocks. One dike splits into two south of Rock- district, but the Gettysburg sill cuts the northwest cor ville and both branches extend into Maryland. ner of the Hanover quadrangle, as shown in plate 16. A dike trending S. 40° E. crosses the Triassic rocks This sill and the enclosing red Gettysburg shale dip and enters the Paleozoic limestones near Botts. In gen 40° NW. eral, dikes trending southeastward are less numerous The probable method of intrusion of the Gettysburg than those trending southwestward. Dikes on the west sill has been discussed by Stose.15 A similar method of ern border of the Hanover quadrangle and in the area intrusion was described for the Yorkhaven diabase sill,18 to the west trend more nearly southward. The directions which crosses the Susquehanna River 10 miles north of of the dikes are controlled by tension cracks, which in York. The fissures' through which the diabase entered places become faults which offset the Triassic sedimen the Triassic rocks are believed to lie near the northwest tary rocks. Two such normal faults parallel to the dike edge of the basin where the greatest amount of progres that passes through Botts, offset the Triassic sedimentary sive sinking and faulting occurred during Triassic dep rocks near Farmers. South of Abbottstown faults that osition. The rising magma broke through the Triassic offset the basal beds of the New Oxford formation trend beds near the vents in the form of cross-cutting bodies, in general S. 10° W. and are approximately parallel to and injected the beds to the southeast in the form of sills. the dikes west of Hanover. In the Lancaster 14 quad The magma extended still farther southeastward as rangle near Salunga (pi. 16), a diabase dike follows a dikes that followed vertical fractures in the Triassic normal fault trending S. 30° E.; north of Marietta sedimentary rocks and continued into the older under Junction, the dike turns south along another fault for a lying rocks southeast of the limits of the basin of Trias half mile, then bends again southeastward along a third sic sedimentation. Some of these dikes in the area south fault, which continues S. 20° E. across the quadrangle, east of the Triassic outcrops may have been feeders of then changes its direction to S. 35° W. in the northern large diabase bodies in Triassic sedimentary rocks that part of the McCalls Ferry quadrangle and passes are now removed by erosion, but evidence is not available through Safe Harbor and across the southeast cor to support such a view. ner of the district and thence southwestwarcl across Maryland. These dikes and the normal faults that they CHARACTER OF THE ROCK follow or parallel represent major lines of Triassic frac The diabase in the dikes is a fine- to medium-grain ?,d tures. They cut across older structural lines, which are dark-gray to black rock of typical diabasic texture. nearly at right angles to them. Many of the diabase The chief constituents are grayish-green plagioclrse dikes originate in or join the diabase sills to the north (andesine or labradorite) mostly in lath-shaped grains west (pi. 16), cross the Triassic sedimentary rocks, and persist for many miles across the older rocks. The Con- 36 Stose, G. W., Triassic igneous rocks in the vicinity of Gettysbrrg, shohocken and Downingtown dikes, 35 miles east of Pa. : Geol. Soc. Amer. Bull., vol. 27, pp. 625-630, 1916. Fairfield- Gettysburg folio, TT. S. Geol. Survey Geol. Atlas (No. 225), pp. 11-12, the district, are 60 to 70 miles long; and the Safe Harbor 1929. 16 Stose, G. W., and Jonas, A. I., Geology and mineral resources of the 14 Stose, G. W., and Jonas, A. I., Lancaster quadrangle, Pa.: Pennsyl Middletown quadrangle, Pennsylvania : U. S. Geol. Surv. Bull. 840, pp. vania Geol. Survey, 4th ser., Topog, and Geol. Atlas No. 168, p. 55, 1930. 41-43, 1933. 462857—44———5 58 GEOLOGY OF THE HANOVEK-YOKK DISTRICT, PA. and interstitial green augite; other minerals that can be Palisade diabase is ascribed by Lewis 21 and Bowen 22 to seen only in thin section are magnetite, apatite, and a gravitative differentiation of basaltic magma. The little quartz. Augite is more abundant than feldspar in differentiation resulted in the segregation of a part the fine-grained diabase. richer in feldspars, probably more sodic in composition, The diabase of the Gettysburg sill where it crosses and rich in mineralizers, which in many places escaped the northwest corner of the Hanover quadrangle, is fine into the adjoining sedimentary rocks. The normal fine grained at the borders. On the southeastern edge in the grained diabase in the chilled contact layer at the top lower part of the sill, this fine-grained diabase grades of the sill represents original magma that solidified upward into a lighter-gray medium-grained diabase in before differentiation took place. the center. The upper part of the sill contains a coarse- METAMORPHISM OF WALL ROCK and medium-grained pink sodic differentiate of the Above and below the sills, the adjacent red shale and diabase. The coarser-grained layer is about 10 feet sandstone are altered to a dense bluish-black porcel- thick and grades upward into a medium-grained pink lanite, and the lighter-colored pinkish-gray sandstone is f acies. The coarser-grained variety is composed largely altered to white or green quartzite. The width of out of pink feldspar crystals with green hornblende laths crop in the altered rocks is usually half a mile, but arranged in part as radiating sheaves. Epidote occurs where the beds dip less than 30° it is wider. These hard also in sheaves and in veins. In the upper finer-grained baked rocks grade through a narrow belt of purple part of this differentiate, the amount of hornblende ex shale and sandstone into the normal red rocks of the ceeds that of feldspar. The dark olive-green crystals of Triassic. In the northwest corner of the Hanover quad hornblende are as much as 1 inch long. The fine rangle, the sill and the enclosing sedimentary rocks dip grained rock is cut by coarse-grained aplite. The top 40° NW. and the outcrop of the altered rock, is only of the sill is typical fine-grained dark-gray diabase. a quarter of a mile wide. The altered shale and The feldspar of the pink pegmatitic f acies is twinned sandstone are recrystallized and contain nev^ minerals sodic oligpclase whose composition is close to that of introduced by hot waters that escaped from tH diabase. albite.17 It is clouded by fine bands of saussurite paral In the Hanover quadrangle, epidote and chlorte nodules lel to the twinning lamellae and contains minute flakes weather out on the surface as round knots. In the of sericite. The hornblende is fibrous and penetrates grayish blue baked shale above the sheet, cavities and the oligoclase along edges and cracks. Bluish-green veins are filled with the white zeolite, heulandite, and hornblende, of the variety pargasite, occurs in some green copper carbonate coats the shale in places. specimens. The pink facies contains also epidote fibers In thin section, the recrystallized shale is seen to be and abundant titanite in grains and crystals. The made up of fine quartz and feldspar grains in a ground- oligoclase, banded with saussurite, is an alteration prod mass of felty sericite and minute granuler of black uce of a more calcic feldspar. Hornblende probably is iron oxide. Epidote prisms occur on the borders of secondary to augite, although no augite was observed heulandite. Irregular rounded nodules of green horn in the sections studied. These minerals are character blende with inclusions of quartz spot the rock. The istic of light-colored diabase differentiates elsewhere. Triassic sedimentary rocks were not only recrystallized Light-colored rock composed of pink feldspar and horn but were permeated by mineralizing solutions that con blende also occurs near the top of the Yorkhaven 18 dia tributed chiefly lime and magnesia to the formation base sill in the Middletown quadrangle, and in the of these minerals. The mineralizing solutions came Gettysburg sill at several localities in the Gettysburg from the magma, and, during its crystalization, were and New Cumberland quadrangles. The differentiate released into the adjacent sedimentary rocks. The con has been more fully described in the report on York sequent reactions aided in the induration and metamor- County.19 Near Gettysburg, Lewis noted titanite in the phism of the sediments. aplite facies. In the Saint Peters sill, the pegmatitic In the New Cumberland quadrangle north of the facies 20 is a hornblendic rock associated with magnetite Hanover quadrangle, limestone pebbles in cor^lomerate ores. beds of the Conewago member of the Gettysburg shale In the Gettysburg sill and elsewhere these differen have been dissolved, leaving rounded cavities that con tiates are near the upper part of the igneous body. In tain trapezohedral crystals of the iron garnet, andradite. New Jersey, pegmatitic facies in the upper part of the (See pi. 15, Z>.) In the Gettysburg quadrangle to the west and at Dillsburg in the Carlisle quadrangle to the 1T The minerals in the diabase were determined by J. J. Glass. 18 Stose, G. W., and Jonas, A. I., Geology and Mineral Resources of the northwest, magnetite deposits have been f orned by the Middletown quandrangle, Pa., U. S. Geol. Surv. Bull. 840, p. 44, 1933. replacement of limestone at its contact with the diabase. 19 Stose, G. W., and Jonas, A. I., Geology and Mineral Resources of York County, Pennsylvania. Pennsylvania Geol. Survey, 4th ser., Bull. 21 Lewis, J. V., Petrography of the Newark igneous rocks of New C 67, pp. 127-130, 1939. Jersey: New Jersey Geol. Survey Ann. Rept., 1907, pt. 4, pp. 99-167. 30 Smith, L. W., Magnetite deposits of French Creek, Pennsylvania: 22 Bowen, N. L., Adirondack intrustives: Jour. Geology, rol. 25, p. 510, Pennsylvania Geol.' Survey, 4th gar.. Bull. M 14, pp. 35-37, 1931. 1917. GEOLOGIC STRUCTURE 59 QUATERNARY SYSTEM PRE-TRIASSIC STRUCTURE Alluvium.—Alluvium covers the flood plains of the GENERAL STRUCTURE larger streams in the district, but in most places it was The Hanover-York district lies in the southeastern not mapped because of its limited extent. Alluvium- part of the belt of Appalachian folding, where the p**e- covered flood plains occur at intervals along Codorus Triassic rocks were recrystallized or metamorphose^ as Creek and its larger branches, and along Fishing Creek well as folded. The pre-Triassic rocks form the surface and the North Branch of Muddy Creek. Between these of the whole York quadrangle and three-fourths of the areas of flood plains, the streams occupy steep-sided Hanover quadrangle. The major structural units in gorges with little or no alluvium. Below the junction of these rocks are the Pigeon Hills and Hellam Hills anti- South Branch and East Branch of Codorus Creek, an clinoria, Wrightsville'syncline, Stoner overthrust, p.nd unusually wide tract covered with gravel has been the Martic overthrust. (See structure sections, pi. 1.) mapped. Another wide area of gravel borders the The Pigeon Hills anticlinorium and the Hellam Hills stream in the lowland south of West York and York; anticlinormm are uplifts along the same axis, and br:ng but it was omitted from the map, so that the intricate to the surface cores of pre-Cambrian volcanic rocks, bedrock geology would not be hidden. Alluvium and which, with the overlying Lower Cambrian quartzose terrace gravels are well developed and have been mapped rocks, form the higher hills north of the Hanover-York along Conewago Creek in the northwest corner of the Valley. (See fig. 28.) Only the southwest end of the Hanover quadrangle. southern (Mount Zion) anticline of the Hellam Hills Alluvium and soil cover the wide, flat limestone low anticlinorium enters the area. lands of the York-Wrightsville Valley and the lowlands The Wrightsville syncline, which incloses Lov^er at Spring Grove, Nashville, Hanover, Penn Grove, and Cambrian and Ordovician (?) limestones in the York in the Jefferson syncline. The soils of these lowlands Valley, lies south of the Mount Zion anticline and north are largely the weathering products of limestone, are of the Strickler anticline. In this district the Strickler exceptionally fertile, and are highly cultivated; rock anticline is in large part overridden by the Stoner over- outcrops are scarce. thrust. Southwest of York, in the Hanover Valley, Terrace gravels.—Terrace gravels 20 to 60 feet above several anticlines in the Lower Cambrian rocks occur the stream were mapped on flat-topped spurs in mean between the Pigeon Hills anticlinorium and the Sto.ner ders of C'onewago Creek, in the northwest corner of the overthrust. (See pis. 1 and 17.) Hanover quadrangle. Terrace gravel, 60 to 80 feet The Stoner overthrust block is made up of several above Codorus Creek, was observed and mapped at only anticlines in Lower Cambrian quartzites and slates—the one place south of West York. No other terrace gravels Mount Pisgah, Holtz, Kraft Mill, and Berkheimer were found at this level; but lower terrace gravels, which School anticlines. The East Prospect and Jefferson were not mapped, occur on many stream meanders. synclines lie near the southern edge of the Stoner blo^k No high-terrace gravels were observed in this area, The Martic overthrust bounds the East Prospect syn but level-topped hills correspond in altitude with gravel- cline, Holtz anticline, and Jefferson syncline on the covered terraces in the Hellam Hills and along the Sus- south. The Martic block, containing schists of the quehanna River in the adjacent Middletown quadrangle Glenarm series, has overridden the Paleozoic limestones and formerly may have been thinly covered with gravel. and dolomites along the Martic overthrust. Th?se schistose rocks were later folded into the Tucquan arti- GEOLOGIC STRUCTURE cline, which crosses the southeast corner of the area, and The structure of the Triassic rocks in the northern other minor anticlines to the northwest. The Yoe and part of the area and that of the Paleozoic and older rocks Wentz synclines enclose Marburg schist and associated to the south are so different that they will be described quartzites and conglomerates. separately. The Paleozoic rocks were compressed into AREA NORTH OF MARTIC OVERTHRUST close folds that trend northeastward. Many of these folds are overturned and broken by thrust faults along PIGEON HILLS ANTIOLINORIUM which the rocks have moved northwestw ard. The Trias The Pigeon Hills fold is compound and consists of sic rocks, which were deposited after the Paleozoic rocks two large anticlines—a main one lying to the north were deformed, are not folded but were tilted rather west, and a smaller one, with two still smaller anticlinal uniformly northwestward and broken into blocks that folds on its south flank, lying to the southeast. (P^e were displaced by normal faults. These faults have pi. 17.) The anticlinorium is cut by several transverse affected also the rocks of the Paleozoic area and thus faults, which are of later date and offset the anticlines. have somewhat modified the earlier structures. The faults will be described under Triassic structure. 60 GEOLOGY OF THE HANOVEIR-YORK DISTRICT, PA. HIGH ROCK ANTICLINE of Nashville, where it is terminated by the Gnatstown The main uplift, called the High Rock anticline, ex overthrust. Northeastward the overthrust cuts across poses a core of pre-Cambrian metabasalt (greenstone) the Vintage dolomite and the Kinzers formation on the in an area 5 miles long, extending from the western south limb of the anticline. The northeaster'y exten edge of the Hanover quadrangle to a point east of Maple sion of the Gnatstown overthrust is described later. Grove School. The fold plunges both to the southwest ANTICLINES SOUTH OF THE PIGEON HILLS and to the northeast, and the Cambrian quartzites sur round each end. The southwest end of the fold extends South of the Gnatstown anticline, three short anti V/z miles west into the adjacent Gettysburg quadrangle, clines, each with a core of Harpers phyllite, are sur where it is abruptly terminated by the plunge of the rounded by the Antietam quartzite. These- are the fold and normal faults with downthrow to the west. At Menges Mills anticline, a nearly complete fold, which the northeast end, the anticline divides into two arms. plunges both northeastward and southwestward; the The northern arm is largely concealed by the overlap Ambau anticline, another nearly complete fold, which ping Triassic rocks and its east end is terminated plunges northeastward, is cut off at the west by the abruptly southeast of Farmers by normal faults with Iron Ridge cross fault, and is overridden on the south downthrow to the east. The southern arm pitches east side by the Stoner overthrust; and the Mt. Carmel eastward and terminates near Roth Church in the sym School anticline west of the Iron Ridge cros? fault, a metrical arc of Antietam quartzite which dips beneath double fold, which plunges southwestward and may the Vintage dolomite of the lowland. The shale at represent the two anticlines east of the cross fault. the base of the Kinzers formation, which overlies the Anticlinal hills of Antietam quartzite northeast of the Vintage dolomite, makes a parallel curved hill 1 mile end of the Menges Mills anticline represent another farther out in the valley; and the upper sandstone of uplift along that same general axis. The short east the Kinzers, an outer curved hill. A longitudinal fault ward trending shale hill north of Nashville is composed near the middle of the fold has downthrow to the south of the lower member of the Kinzers formation on the so that the Lower Cambrian section is not complete on north flank of the Menges Mills anticline. A longitudi the south limb. The fold is covered on its north side nal fault along the northwest side of Menges Mills anti by Triassic rocks which overlap onto the pre-Cambrian cline cuts off abruptly the west end of this shale hill at rocks. Nashville; and the east end is similarly truncated by another longitudinal fault. These longitudinal faults GNATSTOWN ANTICLINE AND OVERTHRUST are younger and are described more fully under Triassic The axis of the second anticline in the anticlinorium structure. passes through Gnatstown and, therefore, is called the Three small linear hills of Antietam quartzite in the Gnatstown anticline. (See pi. 17.) It is broken on limestone lowland east of Nashville represent another its north side by a thrust fault, called the Gnatstown uplift on the general axis of the Menges Mills anticline. overthrust, and overrides the High Rock anticline to the These low hills, with deep-red sandy soil der'ved from north. The basal conglomerate of the Hellam member uppermost beds of the Antietam quartzite, stand out and the underlying metabasalt are brought up in the prominently in the limestone lowland. T'e south core of this anticline along the Gnatstown overthrust east sides of the hills are cut off abruptly by a fault that 1 mile southwest of High Rock and probably also at has dropped the limestone of the middle n: ember of Gnatstown; but the metabasalt, if present, is hidden by the Kinzers to the level of the Antietam quartzite. An quartzite talus. Springs along this fault southwest of iron ore pit lies on this fault. High Rock are the source of the Hanover water supply. Members of the Chickies quartzite and the Harpers SPRENKEL SCHOOL ANTICLINE phyllite appear in normal sequence on the south limb Aii anticline marked by a belt of hills composed of the western part of the anticline. Higher beds are largely of Kinzers formation extends from Spring cut out by a longitudinal fault along the south side of Grove northeastward for 6 miles and is called the the fold. Northeast of the Iron Ridge cross fault, Sprenkel School anticline. It divides the limestone which is described later, Cambrian rocks, from the Hel area of the valley southwest of York longitudinally into lam conglomerate member of the Chickies quartzite to two narrow lowlands. Along the axis of the fold, Vin the Harpers phyllite, are exposed in a nearly symmetri tage dolomite comes to the surface at two places, one cal northeastward-pitching fold, broken on its north northeast of Spring Grove, and the other north of limb by the Gnatstown overthrust. Northeastward the Sprenkel School. The lower shale member of the Kinz fold bifurcates, and the Chickies quartzite in the north ers formation, exposed in rows of low hills, entirely sur ern arm extends more than a mile beyond its southern rounds the dolomite; and the ends of the fold pitch arm. The Antietam quartzite on the south limb of steeply northeastward and southwestward. Along the this part of the anticline extends V/2 miles northeast Gnatstown overthrust, the Kinzers formation on the GEOLOGIC STRUCTURE where it crosses Pottery Hill 1 mile southwest of West York. In the quarry the thrust plane dips 55° SE., and Harpers phyllite is thrust on Ledger dolomite, Hiich makes the lowland to the northwest. (See fig. 23 and pi. 18, B.} Northeastward the Gnatstown overthrust is not clearly traceable in the city of York, but a possible further extension of the fault is discussed in connection with the Mount Zion anticline. MOUNT ZION ANTICLINE The Mount Zion anticline is the southern fold cf the Hellam anticlinorium, and is largely in the Middletown quadrangle, north of the Hanover-York district. As Pottery described in the report on the Middletown quadrangle,23 ( Gnatstown Hil'l the Hellam anticlinorium is composed of four anticlines lover-thrust Ledger named the Chickies Rock, Trout Run, Accomac, and dol. Mount Zion. Another fold just west of the Accomac anticline is now recognized as the Dugan Run anticline. (See fig. 24.) West and south of the Trout Run anti cline are the Emigsville and Dee Run synclines. (See FIGUEB 23.—Sketch of plan and section of the Gnatstown overthrust Pl.17.) exposed in a small quarry along Lincoln Highway on Pottery Hill, The Mount Zion anticline pitches southwestwarcl and southwest of York: A, Plan of the thrust fault, showing Harpers phyllite, with cleavage dipping 50° SE., overriding Ledger dolomite; only its westward-plunging end'enters the York cniad- B, Section across the fault. rangle. Pre-Cambrian metabasalt is exposed in the core of the anticline northwest of Hellam in the Middletown north flank of the anticline overrides the Ledger dolo quadrangle. Metabasalt and associated aporhyolite are mite and Conestoga limestone. South of West York, exposed in the core of the Accomac anticline soutlwest the small Pottery Hill anticline lies north of the east of Accomac; and on the highway just south, metabasalt end of the Sprenkel School anticline. The axis of the is closely folded, and the minor folds are overturned to Pottery Hill anticline trends east; and Harpers phyllite the northwest. Along the south bank of the Susque- in the core is surrounded by Antietam quartzite, with hanna River west of Accomac (see fig. 24), aporhyolite Vintage dolomite on the southeast flank. This anticline and the Hellam conglomerate member of the Chickies is cut off on its west and north sides by the Gnatstown overthrust. The thrust plane is exposed in a small 23 Stose, G. W., and Jonas, A. I., Geology and mineral resources of the Middletown quadrangle, Pa.: U. S. Geol. Surrey Bull. 840, pp. 50-53, quarry on the south side of Lincoln Highway (U. S. 30) 1933. 76'40' Pre-Cambrian rocks Antietam quarbzite T, OverLhrust side Harpers phyllite (Continued at left) FIGURE 24.—Revised geologic map of the Mount Zion and Accomac anticlines in the Middletown quadrangle, showing the Glades and High- mount overthrusts. Specimen of mylonite from the Highmount fault, illustrated in plate 18, A., was obtained just east of Accomac, 62 GEOLOGY OF THE HANOVE'R-YORK DISTRICT, PA. quartzite on the north limb of the Accomac anticline are ers phyllite south of the fault is cut out, and Antietam overturned and dip 35° SE. These rocks are much quartzite is at the contact. In the closely folded Antie sheared in the vicinity of the Glades overthrust on the tam quartzite near the fault the bedding planes have northwest side of the fold. been largely transposed to the direction of the cleavage, which dips 45° SE. Beyond this point the,fault bends GLADES OVERTHBUST sharply northward across the structure, and at High- The Accomac and Mount Zion anticlines override the mount crushed and veined Chickies quartzite is in con Dugan Run anticline along the Glades overthrust. tact with gently dipping basal beds of the Hellam mem This thrust relationship is well shown in the stream ber and underlying metabasalt in the core of the Mount gorge l^miles northwest of Hellam. (See fig. 24.) In Zion anticline. The fault contact is exposed in a small an embayment in the front of the overthrust at this ravine just south of Accomac. (See fig. 24.) Here point, pre-Cambrian metabasalt and basal beds of the finely laminated gray slate with thin quartzite layers, Hellam conglomerate member of the Chickies quartzite belonging to the upper part of the Chickies quartzite, cut off and lap around the severed ends of Chickies is in contact with and overlies schistose metabasalt in quartzite beds in the Dugan Run anticline. Details of which the cleavage dips 45° SE. The quartzose banded the structure here are shown in figure 24. slate is minutely folded and mylonitized (see pi. 18, A) ; In the vicinity of Glades, upper beds of the Hellam and the cleavage, parallel to the axial planes of the conglomerate member are thrust across the Harpers folds, dips 45° SE. The metabasalt at the fault contact phyllite and Antietam quartzite; and 1 mile west of is also sheared to a schistose mylonite. The fault plane, Glades, the Chickies quartzite is thrust over Vintage accompanied by a quartz vein near the cor tact, dips dolomite. At Codorus Creek the Glades overthrust is 45° SE. overridden apparently by the Highmount overthrust. The preceding evidence indicates that the Highmount The rocks are well exposed in a small ravine just west fault is not a normal tension fault but is a tl rust fault of Pleasureville. (See fig. 4.) On the north side of the that was formed under compression. The southeast ravine, massive Chickies quartzite forms a rocky hill in ward dipping cleavage, brecciation, and veining of the which the beds strike southwestward toward the lime rocks of the southeast side of the fault, and the less stone in the lowland northwest of the fault; and south disturbed condition of the Hellam conglomerate north of the ravine, the upper slate and quartzite of the Hellam west of the fault suggest that the rocks to the southeast member strike parallel with the massive Chickies quartz were thrust northwestward along a fault that dips 45° ite. Near the overthrust the hard beds of the thrust SE., as shown in the exposure near Accomac. block are broken and veined with quartz, and the slaty The Hellam Hills uplift, which in earlier studies layers are closely folded. appeared to be a single anticline with an overthrust fault on its northwest side and uplifted on its south side HIGHMOUNT OVERTHRUST along a normal tension fault, is in reality two anti The southeast side of the Accomac and Mount Zion clines and an intervening syncline, the southern anti anticlinal block is bounded by a slightly curved fault cline having been thrust northward and suf ^rimposed trace. On the south side of the Mount Zion anticline, on the northern one. The diagrammatic map (fig. 25) the Harpers phyllite on the south is in fault contact shows the postulated folds before faulting. The north with various beds of the Hellam conglomerate to the limb of the northern fold, the Mount Zion anticline, was north. From the evidence at hand in 1933 24 the fault strongly overturned and broken, and the anticline was was considered to be a normal tension fault downthrown pushed northwestward along the low-dipping Glades to the south and was called the Highmount fault. How overthrust, which cuts diagonally across the beds from ever, in two places near the north edge of the York the pre-Cambrian rocks in the core of the fold north quadrangle and at a point north of Stonybrook in the west of Hellam to the Chickies quartzite at the westward- Middletown quadrangle, small masses of crushed, plunging end of the fold at the Codorus gorge. The veined, and sheared Chickies quartzite lie next to the southern fold, the Chickies Rock anticline, vas broken phyllite at the fault contact. Southeastward-dipping by the Highmount overthrust, which cuts out much of planes of schistosity are strongly developed in the phyl the north limb of the fold, so that south-dipping beds lite and the quartzite at these places, and bedding is not of the south limb were thrust northwest over the inter evident. Northeastward in the Middletown quadrangle vening syncline and came to rest on the souti flank and the fault separates basal beds of the Hellam conglom the core of the Mount Zion anticline. Younger rocks erate member and underlying pre-Cambrian metabasalt were thus thrust over older rocks. The Highmount in the core of the Mount Zion anticline from the Harpers fault is steeper, and consequently its trace is straighter phyllite on the south. Northwest of Hellam the Harp- than that of the Glades overthrust. Toward the east 84 Stose, G. W., and Jonas, A. I., Geology and mineral resources of the the fault cuts diagonally across the structure to the north Middletown quadrangle, Pa.: U. S. Geol. Survey Bull. 840, pi. 1, 1933. side of the anticline in Roundtop and ChicVies Rock. GEOLOGIC STRUCTURE 63 At the westward-plunging end of the Chickies Kock 4). In the northern part of Tork the shale on P"os- anticline, north of York, the Highmount fault appar pect Cemetery Hill and on the hill to the east is the ently breaks across the axis of the fold, and cuts upward basal member of the Kinzers formation at the plunging through the Harpers phyllite, Antietam quartzite, and end of the Chickies Bock anticline, and the interrupted Vintage dolomite into the Kinzers formation on the exposures are due to fragmentation of the fault bTock north limb of the anticline at Myers Mill. (See fig. 25.) during overthrusting. Likewise the irregularly dis-v The Kinzers formation south of Emigsville (see fig. tributed masses of limestone, together with fragments 24) dips 10° S. and is greatly overturned, and the lime of the lower shale and upper sandstone members of stone of the middle member of the Kinzers formation is the Kinzers formation, which are surrounded by Ledger thrust over the Vintage dolomite in the Emigsville syn- dolomite west of York (see pi. 1), are apparently ero cline. West of Pleasureville the Highmount thrust sion remnants of the Highmount overthrust *Wock mass overrides the end of the Glades thrust block and resting as klippen on the Ledger dolomite of the over extends beyond onto the Vintage dolomite. (See fig. ridden block. Confirming this interpretation, in most —-__\ 1 v Limestone Z quartzite (Oi.Hellam conglom erate member ) Vintage dolomite Position of overthrus-t fault in fold before break occurred Antietam Present position of quartz'rte overthrust fault (Continued afriqhl) FIGURE 25.—Theoretical restoration of folds of the Hellam Hills anticlinorium before they were broken and overthrust. Original position of the Glades thrust block on north limb of the Mount Zion and Accomac anticlines and its present position overriding the Dugan Run anticline to the north are shown. Exposed part of the Glades thrust block is indicated by ruled pattern. Original position of the Highmount thrust block on the south side of the Chickies Rock anticline and its present position covering most of the Chickies Rock anti cline and overriding west end of the Mount Zion anticline are indicated. Probable connection of the Highmount and Gnatstown overthmsts, including klippen of Kinzers formation northwest of York, is suggested. Northwest edge of the Gnatstown-Highmount thrust block is indicated by halftone pattern. Present position of the Gnatstown overthrust block on south limb of the High Rock anticline in the Pigeon Hills is shown at left. Amount of movement on overthrusts is not known. 64 GEOLOGT OF THE HAN'OVE'R-YORK DISTRICT, PA. places the rocks of the Kinzers formation in these East of York Conestoga limestone is generally at the remnants are closely folded and contorted, whereas surface. Northeast of York, on the north side of the the Ledger dolomite of the overridden block is only syncline, the Lower Cambrian limestone formations gently folded. dip south from the Mount Zion anticline and pass be If this is the correct interpretation of the structure, neath the Conestoga limestone, which also dips south the Highmount fault was once continuous around these ward. On the south limb of the syncline these detached masses from the Kinzers formation and Cambrian formations rise from beneath the Conestoga joined the Gnatstown overthrust exposed on the north limestone but still dip southward because the beds are side of the Pottery Hill anticline. (See fig. 25.) Block overturned. South of Wrightsville at the Susque- faulting in the thin overthrust plate and later erosion, hanna River, the Lower Cambrian formations on the however, make it difficult or impossible to trace these north limb of the Strickler anticline emerge from be faults into one another. neath the Stoner overthrust and are likewise overturned RELATION OF THE PIGEON HILLS, HELLAM HILLS, AND BLUE and dip southward. RIDGE-CATOCTIN MOUNTAIN ANTICLINORIA In the southern part of York near the certer of the The Pigeon Hills and Hellam Hills anticlinoria (fig. syncline, the Conestoga limestone is well exposed in 26) are evidently local uplifts along the same general brick yards where the disintegrated rock and soil have axis. In the Middletown quadrangle the Hellam Hills been stripped from the bedrock. The thin-bedded lime fold is broken on the north side by the Chickies over- stone is closely folded, and the axial planes of the folds thrust,24 along which Lower Cambrian quartzites have dip uniformly south. The beds on the limbs c f the folds moved over the limestones of the Marietta valley. The have been thinned and the crests and troughs thickened overthrust is covered by the overlapping Triassic rocks by the differential movement of material. (S?e fig. 19.) south of Mount Wolf in the Middletown quadrangle. Southwest of York, the Conestoga limestonr- has been The Pigeon Hills anticlinorium similarly is believed to uplifted in minor anticlines and eroded io:;' ly; but be overthrust on its north side; for, if resistant Cam it continues southwestward to a point sout1! of Bair, brian quartzites were present on the north limb of the beyond which Ledger dolomite is exposed at the surface fold during Triassic deposition, hills equal in height to in the syncline. The part of the syncline exposed north the main Pigeon Hills should occupy the area? instead of the Stoner overthrust at Spring Grove is very of the depression that forms the floor of the adjacent narrow. To the southwest the syncline is further con Triassic rocks. The Triassic rocks in this area probably stricted by the Ambau anticline, and is terminated by lie mostly on limestone and cover the postulated thrust the uplift along the Iron Ridge cross fault. The Han fault that may be the southwesterly extension of the over Valley is another broad syncline along the same Chickies overthrust along the original northwest base general strike, and incloses tightly folded Conestoga of the Pigeon Hills. limestone. The folds are probably also overturned In the Fairfield, Pa., quadrangle 25 and the Emmits- to the north, but exposures in this lowland are few and burg, Md., quadrangle west and southwest of this dis poor. trict, a broad anticline of pre-Cambrian volcanic rocks STRICKLER ANTICLINE flanked on both sides by Lower Cambrian quartzites The Strickler anticline lies south of the Wrightsville forms the Blue Ridge-Catoctin Mountain anticlinorium. syncline. (See pi. 17.) In the southeast corner of A branch of this fold trends northeastward toward the the Middletown quadrangle, the anticline is well ex Pigeon Hills anticlinorium, but is terminated abruptly posed in the west bank of Susquehanna River. Antie- by the normal fault, which crosses the trend of the pre- tam quartzite forms the core of the anticline, and Triassic structures, along the west side of the Triassic Vintage dolomite and the lower shale meirber of the basin. Although these two anticlines are separated by Kinzers formation lie on the flanks. The anticline is a belt of Triassic rocks about 25 miles wide, they lie largely concealed in the Hanover-York ar°,a by the probably on the same general axis of uplift and were Stoner overthrust. The Lower Cambrian formations separated by the downwarping of the Triassic basin and on the north limb of the anticline are exposed along by post-Triassic normal faulting along the western the south side of the valley from Plank Road northeast border of the Triassic sediments. (See fig. 26.) to the edge of the York quadrangle. WRIGHTSVILLE SYNCLINE STONER OVERTHRUST The Wrightsville syncline occupies the Hanover-York The Stoner overthrust follows the northwest edge Valley underlain mainly by limestone. (See pi. 17.) of the wide area of the Lower Cambriar quartzose 24 Stose, G. W., and Jonas, A. I., Geology and Mineral resources of the rocks, exposed south of the Hanover-York Valley, from Middletown quadrangle, Pennsylvania: U. S. Geol. Survey Bull. 840, a point near Stoner Station, at the north edge of the pp. 51, 54-56, 1933. 28 Stose, G. W., Fairfield-Gettysburg folio: U. S. Geol. Survey, Geol. York quadrangle, southwestward to the vicinty of Atlas (no. 225), Fairfield geologic map, 1929. Hanover. (See pi. 17.) The overthrust has not been GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 17 77*00' 76*45' 76*30' 76*15 HANOVER QUADRANGLE cCALLS FERRY QUADRANGLE ProspeVt EXPLANATION Overthrust fault T.overthrust side Axis of anticline Axis of overturned anticline _ _ _*_ _ _ 39'XBETTYSBURG QD Axis of syncline 45 TANEYTOWN WESTMINSTER QUADRANGLE PARKTON QUADRANGLE Axis of overturned syncline P E N N S Y] LVA N I B Miles MARYLAND MAP OF THE HANOVER-YORK DISTRICT AND ADJACENT REGION, SHOWING MAJOR STRUCTURAL AXES AND THRUST FAULTS NORTH OF THE MARTIC OVERTHRUST. Normal faults, except the larger transverse ones that offset the thrusts, are omitted. Structure lines south of Martic overthruat are shown in figure 27. (Face p. 64 *•" Ms O" rt- £3gS (P 0> P h- 66 GEOLOGY OF THE HANOVER-YORK DISTRICT, PA. actually observed, but structural evidence of its presence All the rocks of the Stoner overthrust block are closely is convincing throughout most of its course. The over- folded, and the axial planes of the folds dip southeast thrust nature of this contact is not clearly indicated in ward. At several places the rocks of the tl rust block places where the Conestoga limestone lies next to the and the rocks they override have been seen in the same fault, because the relationship between the Conestoga outcrop, but the contact was hidden. In the cut on and the adjacent Harpers phyllite or Chickies slate the Pennsylvania Railroad east of the highway to Brill- may be mistaken for the unconformable overlap that hart, the Harpers phyllite on the front of the Stoner elsewhere is known at the base of the Conestoga overthrust is closely folded, and the folds are in part limestone. From Plank Eoad northeastward for 6 sheared out. The most evident structure is a wavy miles, however, a narrow band of Kinzers formation, foliation that dips 45° SE. Imperfectly developed Vintage dolomite, and Antietam quartzite emerges transverse cleavage cuts the foliation at a steeper angle. from beneath the Conestoga limestone on the southeast Farther southeast, quartzose beds in the Harpers phyllite limb of the Wrightsville syncline; and the overthrust is and the underlying Chickies slate are cloroly folded evident. Northeast of the district, in the Middletown and the folds are overturned northwestward. (See quadrangle,26 the overthrust is better demonstrated, for figs. 6, 7.) Structure is similar at the edge of the over- the Stoner overthrust swings southeastward across the thrust mass south of Plank Road. There, Harpers pnyl- structural trend and reveals the Strickler anticline, as lite is thrust over a syncline of Vintage dolomite and shown in plate 17. East of Susquehanna River the Antietam quartzite and only 50 feet of the Antietam Manor anticline, which is the northeastern extension of is exposed next to the fault in the cut of the Maryland the Mount Pisgah anticline, is thrust over the Strickler and Pennsylvania Railroad. The beds of the Antietam anticline along the Stoner overthrust. Still farther and the Vintage are vertical. eastward, the Stoner overthrust is lost to sight in the The sinuous outline of the Stoner overthrust south Conestoga limestone south of Lancaster. At Plank west of York, especially north of Smiths Station, and Road and south of West York, the Stoner overthrust the small outliers that rest on Vintage dolomite west is offset by cross faults. of Jacobs Mill, indicate a low angle of dip for the thrust West of York New Salem a recess in the fault front plane, which was gently folded during or after thrust is the result of erosion of the thin overthrust mass; and ing. The Harpers phyllite in that area does not show a klippe or outlier composed of Harpers phyllite forms bedding, but lias a closely folded laminated structure a hill that rises above the limestone lowland in the with a transverse cleavage, which in places is crinkled. embayment. Southwest of Lehman, the Harpers phyl In the valley, rocks of the underlying block near the lite is thrust over the southeast limb of the Ambau anti thrust are closely folded and overturned northwestward, cline and cuts across the beds down to the Antietam and cleavage is developed in the weaker strata and in quartzite. The thinness of the overthrust plate is shown some of the harder beds. by the deep recesses in the fault front and the klippen The Stoner overthrust block is about three miles wide. of Harpers phyllite on the limestone lowland west and It is overridden on the southeast side by the Martic south of Jacobs Mills. overthrust block. In the York area the Sooner block At Jacobs Mills the overthrust swings around the end comprises the Mount Pisgah and Holte anticlines of a narrow hill of Harpers phyllite and extends 1 mile and the intervening East Prospect syncline; .In the northeastward up a narrow valley in which Vintage Hanover area it includes the Berkheimer pKhool anti dolomite and Antietam quartzite of the overridden cline, the Stormy Hill School syncline, the Kraft Mill block are exposed. Southeast of Jacobs Mills, a split anticline, and the Jefferson syncline. - in the fault encloses a southward-dipping monoclinal MOUNT PISGAH ANTICLINE slice with Kinzers formation at the top. One mile The Mount Pisgah anticline is a narrow fold that ex southwest of Jacobs Mills overthrust Harpers phyllite tends from the northeastern edge of the are?- southwest- forms a similar promontory, south of which the ward to York New Salem. (See pi. 17.) The anticline overthrust swings eastward for 2 miles around the is closely folded; and the beds dip steeply and are for limestone lowland at Penn Grove, a deep irregular em the most part overturned to the north west, especially bayment in the overthrust front. South of Hanover along the edge of the Stoner overthrust. Tt e repetition the Harpers phyllite is thrust over an anticline in which of beds by folding is well shown in tlie valleys of Kreutz are exposed Antietam quartzite, Vintage dolomite, and and Mill Creeks east of York and in the cliff east of the lower shale member of the Kinzers formation. The Codorus Creek, below the York Country Cl^b. On the overthrust is cut and offset by the Iron Ridge and the highest part of the anticline, northeast of York, the Smiths Station cross faults. basal Hellam conglomerate member of the Chickies slate is exposed in a strip 5 miles long. The Chickies slate is 28 Stose, G. W., and Jonas, A. I., Geology and mineral resources of the Middletown quadrangle, Pa.: U. S. Geol. Surv. Bull. 840, pp. 53-54, 1933. exposed as far southwest as York New Salem and is GEOLOGIC STRUCTURE 67 brought up again southwest of Stovertown in the Berk- the south by the Cabin Creek overthrust, which splits heimer School anticline, which is on the same axis of up off from the Martic overthrust. One mile west of Mar lift as the Mount Pisgah anticline. In the quartzite beds garetta Furnace the limestone in the syncline is cut off of the Chickies slate, anticlinal folds whose axial planes by the Ore Valley overthrust, a split of the Cabin Creek dip 30° to 45° southeast are exposed northeast of York overthrust. The Harpers phyllite on the Ore Valley New Salem and on the grounds of the York Country fault overrides Antietam quartzite to a point north of Club on the east side of East Branch of Codorus Creek. Spry, except at Ore Valley where a narrow strip of lime (See fig. 7.) stone, probably Conestoga, is enclosed in a syncline nert KRAFT MILL ANTICLINE to the fault. Two other shallow synclines of limestone occur in the Antietam quartzite, one south of Delroy The Kraft Mill anticline lies to the south of the and the other along Kreutz Creek south of Golden. Th e Berkheimer School anticline in the Hanover quadrangle one near Delroy is in strike with the Ore Valley syncline. (see pi. 17), and brings up a wide belt of Chickies slate, South of Margaretta Furnace, another syncline er- which extends from a point near Reynolds Mill south- closes Antietam quartzite, a thin band of Vintage dolo westward nearly to Hohf School. In the Kraft Mill mite, and Conestoga limestone. This syncline lies south anticline and also in the Mount Pisgah anticline, the of the strike of the Holtz anticline, and is cut off on the folds are overturned to the northwest; and both the south side by the Martic overthrust. bedding and the cleavage dip mostly southeast. Xhe close folding is exposed in the valleys east of York JEFFERSON SYNOLINE New Salem and along Codorus Creek south of Porters Station. The Jefferson syncline, which encloses Antietam The Chickies slate in the Stoner overthrust block is a quartzite and Conestoga limestone, is south of the Kraft. different lithologic facies of the Chickies quartzite in Mill anticline and extends from a point 2 miles soutl - the anticlines north of the Hanover-York Valley. Over- west of Jacobus southwestward to Smsheim. (See pi. thrusting has brought the slate nearer the quartzose 17.) This syncline lies south of the trend of the Holtz facies, but the amount of movement is not known. anticline and may be the southwesterly extension of the If, as is possible, the Stoner overthrust dies out in the southernmost fold in the East Prospect syncline. limestones east of the Manor anticline, west of Lancaster, A mile southwest of Sinsheim, another downf old along the amount of movement appears not to have been great; the axis of this syncline encloses the Antietam quartzite however, the Mount Pisgah anticline, which contains the and Conestoga limestone in an area about three miles slaty facies of the Chickies, lies 12 or 15 miles northwest long. The main part of the syncline is double and cer of the trend of Mine Ridge anticline, which contains a tains two narrow bands of Conestoga limestone sepa quartzite facies similar to that in the Hellam Hills. If rated by an anticline of Antietam quartzite. At one the basin of deposition of the slaty facies originally lay point on the north side of the syncline, northwest cf southeast of the basin in which the quartzite facies was Seven Valleys, a small area of Vintage dolomite is er- deposited, that is, south of the trend of Mine Ridge anti posed between the Conestoga limestone and the Antietam cline, the slaty facies in the Stoner overthrust has moved quartzite. The Jefferson syncline is overridden on the northwestward at least 15 miles. The writers believe south side by the Marburg schist along the Martic over- that the Glenarm series was carried a great distance thrust. At the western edge of the Hanover quadrangle northwestward on the Martic overthrust and that the a small area of Antietam quartzite is enclosed along this Stoner overthrust block, which lies north of the Glenarm same synclinal axis and lies just north of the Mart?c series, may have been pushed up in front of the advanc overthrust. ing Martic overthrust. HOLTZ ANTICLINE The Holtz anticline is a narrow, closely compressed EAST PROSPECT SYNCLINE anticline which brings Chickies slate to the surface from The East Prospect syncline lies south of the Mount a point ~Ly2 miles west of Margaretta Furnace south- Pisgah anticline in the York quadrangle, and encloses westward to East Branch of Codorus Creek. (See pi. Antietam quartzite and overlying limestone. (See pi. 17.) The fold is compound and is composed of three 17.) The fold deepens to the east, where it merges with minor folds, which plunge at their ends and which are the Lancaster syncline to form a wide valley in the arranged enechelon. . The axis of the main fold passes limestone. The limestones are enclosed in three synclinal through Holtz. At the northeast end the axis of one folds, two north of and one south of East Prospect. The minor parallel fold is half a mile to the north, and at two northern arms, enclosing Kinzers formation and the southwest end another minor fold lies south of Spry. Vintage dolomite above the Antietam quartzite, are in The Cabin Creek overthrust carries the main fold over the valleys of Canadochly Creek and the small stream the northern one. In the area south of Margaretta at Klein School. The southern arm is overridden on Furnace the Antietam quartzite, Vintage dolomite, an d 68 GEOLOGY OF THE HAKOVEIR-YORK DISTRICT, PA. Conestoga limestone are enclosed in a syncline south of trict southwestwarcl through Relay, Jacobus, Seven Val the main fold. leys, Jefferson, and Sinsheim, and thence southwestward The folding in the Holtz anticline is very close, and beyond Fairview School. It passes out of the district the folds are sheared out by steeply dipping transverse li/4 miles north of Raubenstine, and continues south- cleavage. The argillaceous layers form a series of westward across Maryland. In this thrust block, Mar steeply dipping lenses parallel to the cleavage. The burg schist has been carried northwestward over the type of folding observed south and southwest of Mar- Conestoga limestone, the Antietam quartzite, and the garetta Furnace is illustrated in plate 18, G. From Harpers phyllite of the Stoner block. The Martic over- Ore Valley south to Relay along the highway that fol thrust is indicated on the map by a dashed fault line in lows Mill Creek, road cuts show the best and most con localities where Marburg schist has been thrust over tinuous outcrops of the Chickies slate and overlying Harpers phyllite, because the Harpers phyllite some Harpers phyllite in the Holtz anticline. The fold axes what resembles the Marburg schist, and the fault that in the quartzite dip steeply to the southwest. In the separates them cannot be located exactly. Where the softer beds, where folds have been sheared out, nearly Martic overthrust enters the Hanover-York district from vertical lineation parallel to the fold axes shows on the the east, the Marburg schist is thrust over the Cones- cleavage planes. Vertical surfaces show the fold axes, toga limestone in the East Prospect syncline, and just and horizontal surfaces, the cross sections of rock layers. to the west, over the Antietam quartzite and infolded The pitch of the folds ranges from 80° SW. to vertical Conestoga limestone in the Cabin Creek syncline. Three three-quarters of a mile southeast of Ore Valley, but and a half miles from the east edge of the district, the is only 20° to 40° SW. at Relay. On the upland on Marburg schist overrides the Harpers phyllite on the either side of Mill Creek, lack of outcrops prevents south limb of the Holtz anticline; and this relation is tracing the strike of the beds or determining the extent maintained to a point V/2 niiles west of Jacobus, where of steeply dipping folds. This area exhibits on a Antietam quartzite and Conestoga limestone in the Jef small scale a steep fold-axis structure, which is wide ferson syncline lie north of the Martic overthrust. This spread in Maryland.27 syncline is adjacent to the fault in the Hanover quad rangle except southeast of Hanover, where Harpers AGE OF THE STRUCTURAL FEATURES phyllite is at the contact. At the west edge of the quad The folding and the thrust faulting in the district rangle the syncline north of the fault ag^in encloses involved all the Paleozoic rocks, the youngest of which Antietam quartzite. are probably of Ordovician age. The magnitude of The main folds which can be recognized within the these folds and overthrusts and their general parallelism Martic overthrust block in the district are the Tucquan with those of the Great Valley lead to the conclusion anticline and the Yoe and Wentz synclines. The Yoe that they were formed at the same time as the major syncline, southeast of York, is near the front of the over- folds and overthrusts throughout the Appalachian prov thrust block. The Wentz syncline parallels the Yoe ince. These structural features elsewhere affect the syncline; but the Wentz axis, if extended, would pass Carboniferous rocks and, hence, were produced during southeast of the Yoe axis. Both synclines infold the the mountain making epoch that occurred at the close quartzites associated with .the Marburg schist. The of the Carboniferous period. Most of the transverse Wissahickon formation, lying southeast of the Yoe and faults, which cut across and offset the folds and over- Wentz synclines, forms the largest part of the Martic thrusts in the Hanover-York district, are distinctly overthrust block in the district. From a, point near younger and are described under Triassic structure. Brownton southwestward, the Wissahickon formation In the Glades overthrust block north of York, certain encloses narrow bands of metabasalt that probably were transverse faults that do not pass into the overridden brought up on anticlines. Southwest of Glenville, limestones were evidently formed during later Paleo Wakefield marble accompanies the metabaealt. zoic thrusting and represent the fragmentation of the overthrust block. TUCQUAN ANTICLINE MARTIC OVERTHRUST BLOCK The major structural feature in the southeastern part of the York quadrangle is the Tucquan anticline, which GENERAL DESCRIPTION extends along South Branch of Muddy Cr^ek and con The Martic overthrust block occupies the southeastern tinues southwestward to the Maryland lire near Deer part of the Hanover-York district, and is bounded on Creek. The Martic overthrust block was first described the northwest by the Martic overthrust. (See fig. 27.) in the report on the adjoining McCalls Ferry quad It extends from Cabin Creek at the east edge of the dis- rangle.28 In that area the Tucquan anticline, exposing 27 Jonas. A. I., Tectonic studies in the crystalline schists of southeast 28 Knopf, E. B., and Jonas, A. I., op. cit., U. S. Geol, Surv, Bull. 799, ern Pennsylvania and Maryland : Am. Jour, gci., 5th ser., vol. 34, 1937. pp. 71-80, 1929. GEOLOGICAL SURVEY PROFESSIONAL PAPER 204 PLATE 18 A. MYLONTTIZED CHICKIES QUARTZITE FROM SOLE OF HIGHMOUNT THRUST FAULT, HALF A MILE SOUTHWEST OF ACCOMAC. Locality is shown on tigure 24. Transverse cleavage (indicated on the photograph by the nearly vertical lines) dips 45° SE., parallel to the fault plane. C. POLISHED SURFACE OF CLOSELY FOLDED QUARTZOSE HARPERS PHYLLITE B. HARPERS PHYLLITE THRUST NORTHWESTWARD SOUTH OF MARGARETTA FURNACE. OVER LEDGER DOLOMITE AT LEFT, IN SMALL ROADSIDE QUARRY ON POTTERY HILL, SOUTH- Shows vertical Cleavage. Natural size. WEST OF YORK. Exposed fault plane dips 55° SE. EXPLANATION Strike and dip of foliation Axis of cLntichne A Axis of syncline /<-) Axis of overturned anticlin 6 xA Axis of overturned syncline § -—•-Horizontal axis of syncline i ike and dip of transverse eo cleavage PO d * soy Strike and dip of bedding 0 in Paleozoic rocks i-9 d w FIGUKH 27.—Sketch map of the Hanover-York district and adjacent areas, showing structural axes and structure trends in the Martic thrust block and adjoining Paleozoic rocks. 70 GEOLOGY OF THE flANOVEiR-YO.HK DISTRICT, PA. the albite-chlorite schist f acies of the Wissahickon for folded foliation layers with closely-spaced, steeply dip mation, begins as a double arch two miles west of ping, transverse cleavage. Quarryville and crosses the Quarryville and McCalls The Paleozoic rocks of the adjacent Stoner thrust Ferry quadrangles to a point near High Rock, one mile block are closely folded also. The folds anc1 the trans east of the York quadrangle, from which a single broad verse cleavage in them were formed during the later arch continues1 southwestward. The compound fold is Mine Ridge folding, which affected the Mr.rtic thrust the southwesterly continuation of the double anticline of block as well; therefore, no divergence is apparent in Mine Ridge (see figs. 26 and 27), which is developed in the structure in the Paleozoic rocks and that in the Mar- the pre-Cambrian and lower Paleozoic rocks of the over tic block at their contact. ridden block. The Paleozoic rocks plunge southwest- The folds in the Tucquan anticline and on its flanks ward from the nose of the Mine Ridge anticline; and pitch in a southwesterly direction. The pitch averages the youngest formation, the Conestoga limestone, passes 15° but in places the amount is as great as 30°. In a southwestward under the albite-chlorite schist, and the region with pitching folds the strikes curve. In this schists and Paleozoic rocks are folded together. area no beds can be traced because the schist is made up of foliation layers that are not continuous for any DETAILED STRUCTURE distance; the lithology of the schists is similar through In figure 27 the structural trends of the fold axes in out and for the most part outcrops are limited to stream the schists of the Martic overthrust block are based on valleys. The curving strike, however, is indicated by observation of the trends of lineation, which parallel the the variable direction of the strike of the liner.tion. This tectonic axes.29 If outcrops in the schists were more is well seen in the Tucquan anticline. At the Susque- continuous, the trends of the fold axes could be deter hanna River the axis of this anticline trend? S. 70° W., mined more accurately. At the crest of the Tucquan whereas from High Rock southwestward it trends S. anticline, the foliation and the axial planes of those re 40° W. The strike varies considerably also to the south cumbent folds that have escaped destruction are hori east. At Southside and southeast of that point for a zontal or gently inclined. The dips of the axial planes distance of two miles, the strike is nearly north-south; of the recumbent folds and of the foliation formed by and to the southeast, at Bryansville, it again trends S. the shearing out of the folds gradually steepen in oppo 40° W. site directions away from the crest of the anticline. (See GLEN EOCK ANTICLINE fig. 27.) The foliation layers are folded into gentle folds whose axial planes also dip away from the crest. In the Hanover York district the Tucquni anticline These foliation folds have a longer and a shorter limb. is recognized as an upfold because the foliation dips in The longer limb always dips away from the crest, but opposite directions off the anticline. On tl*- flanks of the shorter limb in places dips towards it. In the sec this anticline where foliation dips are overturned, major tion along North Branch of Muddy Creek, the foliation structures in the schists cannot be recognized with cer at Laurel, iy2 miles west of the crest of the arch, dips tainty. Elongate areas of metabasalt are infolded in 20° NW.; at Felton the dip has increased to 45° NW.; the Wissahickon formation northwest of tH Tucquan and northwest of Brownton it is 50° NW. The fold anticline and southeast of the Wentz syncline. The axes of the foliation layers in this section dip southwest- axial planes of the folds in these rocks dip northwest, ward from 10° to 30°. Southwestward along the strike and the amount of dip increases from 35° near Anstine in the valleys of East and South Branches of Codorus to 70° at a point north of Glen Rock. These areas of Creek, the dip of the foliation increases at a similar rate metabasalt and associated Wakefield marb1 ^ near the from south to north. Maryland state line are regarded as anticlinal because The foliation is cut by a transverse cleavage whose in Maryland, where they are more widely exposed, they dip ranges from vertical to 80° NW. or SE. This cleav appear to lie hi large part beneath the albite-chlorite age is parallel to the axial planes of the minor folds and schist f acies of the Wissahickon formation. crinkles, is more prominent in the micaceous layers, and has smooth, straight surfaces in contrast to the somewhat YOE SYNOLINE curved or irregular surfaces of the foliation layers. In the Yoe syncline (fig. 27) the blacl: slate and In the area northwest of a line passing V/2 miles quartzites folded into the Marburg schist are believed to northwest of Brownton, 1 mile southeast of Graydon, be the youngest beds present. In the York quadrangle, and through Glen Rock and Sticks, no recumbent folds the transverse cleavage dips about 80° NW. between were observed. As far as the northwestern edge of the the Tucquan anticline and the axis of the Yoe syncline, Martic overthrust block, the Wissahickon schist, the which passes through Craley. From this axis to the Marburg schist, and the associated quartzites show edge of the Martic thrust block and in th°. Paleozoic rocks to the northwest, the cleavage dips 80° SE. The 29 Gilluly, James, Mineral orientation in some rocks of the Shuswap Terrane: Am. Jour. Sci., 5th ser., -vol. 27, pp. 184-185, 1934. exposures of the rocks in the Yoe synclir^ are very GEOLOGIC STRUCTURE 71 poor because they occupy an upland area. East of the part of the limestone area and forms a hill south of York quadrangle the eastward extension of the syncline an abandoned limonite pit. Twelve miles southwest of passes out of the Marburg schist north of Long Level; the Loganville area, southeast of Zumbrum School, there and, on the east side of Susquehanna River north of is another uplift of limestone on the same general strike Creswell, the syncline is in the Conestoga limestone, as the Loganville anticline. The only outcrop observed which, at that point, lies north of the schists of the in this area was in an abandoned quarry east of the road Martic block. along Codorus Creek, where grayish-white marble was WENTZ SYNCLINE exposed. The Wentz syncline occupies the southern part of the BELATION OF FOLDS IN THE PALEOZOIC FORMATIONS TO THOSE IN T^E Hanover quadrangle. (See fig. 27.) Southwest of the GLENAEM SERIES highway (US 111) the quartzites associated with the On the north flank of the Mine Ridge anticline, the Marburg schist are, infolded in the syncline, and near true thickness and order of the stratigraphic sequence the Maryland state line, where the syncline is deeper, of the Paleozoic rocks that overlie the pre-Cambrian the quartzites are more widespread. The syncline is core of the fold can be determined from their base named from the village of Wentz, in Maryland, 1^ upward in the direction of the pitch. The schists, which miles south of West Manheim, North of the Maryland largely overlie the Conestoga limestones and which are line the main part of the syncline passes through Beecher folded into the Tucquan anticline, also pitch southwest- Hill, Brodbecks, and Huntrick Hill, and quartzite is ward; but the sequence of the schists cannot be dete^- infolded as far northwest as Zumbrum School. In mined, because of isoclinal and recumbent folding and that area the transverse cleavage dips southeastward. the shearing out of the folds, which has greatly modified Northeast of the valley of Codorus Creek toward the the original order of the beds. In this anticline, the northeast end of the syncline, the transverse cleavage Glenarm series and the Paleozoic formations are evi dips northwestward; and this direction of dip persists dently folded together. North of the main body of the northwestward across the strike to the edge of the Martic overthrust block and of the valley underlain by Martic overthrust block. The southeastward-dipping Paleozoic rocks, on the Susquehanna River south of cleavage probably reflects overturning of the folds to Shenks Ferry Station, the schists of the Glenarm series the northwest, and the northwestward-dipping cleavage again appear on the east side of the river and continue reflects overturning to the southeast, although most of from 'Shenks Ferry Station seven miles northward to the exposures are not good enough to verify this Creswell Station. These schists also are folded with suggestion. the underlying Paleozoic rocks, and the fold axes in In a valley near Marburg where the schist is well both series dip southwestward. Because of the south exposed, the dip of the cleavage ranges from 80° NW. to westerly pitch of the folds, erosion has removed the vertical. To the southwest in a parallel valley the schists half a mile east of the river and has exposed cleavage dips southeastward, and this direction of dip the Paleozoic rocks whose folds in the region north of persists northwestward for 5 miles in the northwest Safe Harbor plunge southwestward under the schist. part of the Martic block. The small folds, wherever The axial planes of the folds in both series dip north visible, pitch from 50°-60° NW. Because of the dis west and the closely folded and overturned anticlines continuity of outcrops, the strong development of trans and synclines in the Paleozoic rocks pass southwestward verse cleavage, and the prevailingly uniform micaceous into the schists of the Glenarm series. The metabasslt character of the Marburg schist, the strike cannot be brought to the surface apparently in anticlines ne^.f traced directly; but the pitching folds, wherever ob Glen Rock and north of Shrewsbury Station may lie served, indicate that the strike curves. Curved strike along one of these anticlines which can be recognized has been found in the quartzites to the south where in the Paleozoic rocks. Also the Strasburg syncline may the outcrops are more continuous; and from Brodbecks pass southwestward through Star Rock and into a syn southwestward into Maryland, wherever exposed, the clinal area near Glen Rock. Farther to the northwest folds have inclined fold axes. the Yoe syncline in the Marburg schist appears to extend eastward into the limestone area, north and east of the LOGANVILLE ANTICLINE schist near Creswell Station. There it is called the Blue crystalline limestone in the Loganville anticline, Millersville syncline. The Yoe-Millersville syncline is which lies between the Yoe and Wentz synclines, is not overturned. The bedding and cleavage in the exposed in a narrow valley northeast of Loganville. Conestoga limestone a mile north of Creswell Station (See fig. 27.) In the Marburg schist on the north dip southeastward into the syncline. The schists south side of the valley the fold axes are horizontal, and the of Creswell Station, on the south side of the synclire, axial planes are overturned to the southeast. Folds are well exposed, and the axial planes of the minor pitch 45° SW. in the schist that divides the western folds and the cleavage dip northwest into the synclire. 72 GEOLOGY OF THE HANOVE1R-YORK DISTRICT, PA. On the north side of this syncline and northwestward agrees with Cloos' suggested explanation for the repeti to the Hellam Hills and Pigeon Hills anticlines in the tion of the Paleozoic sequence. Furthermore, she sug Hanover-York district, the folds are symmetrical or gests that it was the northward push of the Martic over- overturned to the northwest. The Yoe-Millersville syn thrust that produced the thrust plates in the overridden cline appears to be a major structure comparable to the Paleozoic rocks, and, as folding continued during the Mine Ridge-Tucquan anticline on the south and the rise of Mine Ridge anticline, the thrust plates were Hellam Hills-Pigeon Hills anticline on tne north. folded with the overlying schists. The trend lines in this part of the area shown on figure 27 therefore rep EVIDENCE OF OVERTHRTJSTING resent the trend of the folded edges of the overthrust If the two superposed sequences are folded together, plates in the Paleozoic rocks. The trends in these over- it may be asked: What is the structural evidence for thrust plates are parallel to those in the overriding the overthrust relationship of the rocks of the Glenarm schists and the trend lines in both sequences were formed series? In the Tucquan anticline of the York area, as in the latter part of the regional folding. has been stated, the schists of the Wissahickon forma The writer concludes that the recumbent folding in tions contain two schistose structures, an older horizon rocks of the Glenarm series is a manifestation of the tal foliation, and steeply-dipping transverse cleavage in movement by which they were extensively displaced later folds. In the discussion of the albite-chlorite and brought, to lie in structural discordance over the schist facies of the Wissahickon formation, evidence was Paleozoic rocks, and that the structures now visible and given to show that the foliation is a "transposition" common to the Paleozoic rocks and the adjoining schist cleavage produced by slipping in closely appressed re of the Glenarm series were produced in both groups cumbent folds so that they are more or less completely during the main upbowing of Mine Ridge. sheared out and destroyed. Both megascopic and mi croscopic recumbent folds in the Wissahickon schist Recumbent folds are found also in the rocks of the are shown in plate 9. The foliation structure, in Glenarm series in Maryland.30 There, this series com which recumbent folds have been partly or entirely prises the Setters formation, the Cockeysville marble, destroyed so that the schist is made up of thinly lam and the oligoclase-mica schist and albite-chlorite schist inated, alternating micaceous and quartzose layers, is f acies of the Wissahickon formation. Recumbent folds shown in plates 10 to 12. The quartzose layers are in occur also in the Baltimore gneiss, which, in Maryland, large part discontinuous and form lenticles completely underlies these formations. Recumbent folding was sug surrounded by micaceous envelopes, and lie parallel to gested 31 also for the major structure of the Woodville the foliation in the schistose layers. If the layers in anticline, Chester County, Pa. the micaceous and quartzose rocks were originally bed The recumbent folds seen throughout the area are on ding, the foliation produced by slipping in the closely a small scale, and the magnitude of the folding cannot appressed recumbent folds is also largely parallel to be determined in the field owing to the insufficient ver the bedding; but, because the original position of the tical extent of the outcrops. The small scale recumbent layers is completely transposed, the foliation layers do folds may reflect a, large-scale structure developed dur not represent a stratigraphic succession. These folia ing the forward movement of the Glenarm series when it tion layers have been crumpled and folded into the was pushed over rocks of known Paleozoic age; hence Tucquan anticline and the minor folds on its flanks, the displacement may have been effected by large-scale coincident with the upfolding of Mine Ridge anticline. recumbent folding. Because the folds are sheared out. North of the Martic overthrust from near Quarry- the forward movement is represented by the sum of these ville to Shenks Ferry and Safe Harbor, the sequence of small movements. A similar type of folding has been Antietam quartzite, Vintage dolomite, and Conestoga described in the Taconic area 32 of New England. limestone occurs in bands repeated several times, with Metamorphism seems to have taken place in the schists trends parallel to the erosional border of the schist. of the Glenarm series during overthrusting and to have (See fig. 27.) At the celebration in September 1939 of continued in the schists and the Paleozoic rocks during the Pennsylvania Geological Survey's Twentieth Anni the rise of Mine Ridge anticline and after Reformation versary under G. H. Ashley as State Geologist, a series was completed. of papers was read on the age and structure of the In the Hanover-York district no exposure? have been Glenarm series. In one of the papers, Ernst Cloos de found of the contact of the Marburg schist and the scribed briefly his conclusions on his structural study of 30 Jonas, A. L., Tectonic studies in the crystalline scMsts of south the Mine Ridge area. He was not then convinced that eastern Pennsylvania and Maryland, Am. Jour. Sci., 5fo ser., vol. 34, the Glenarm series was thrust over the Paleozoic rocks pp. 367-368, 1937. 81 Bailey, E. B., and Mackin, J. H., Recumbent folding in the Pennsyl- of the area but suggested that the repetition of the vanian Piedmont; preliminary statement: Am. Jour. Sci, 5th ser., vol. Paleozoic sequence north and east of Shenks Ferry may 33, pp. 186-190, 1937. ^Prindle, L. M., and Knopf, B. B., Geology of the Taconic quad represent a series of overthrust plates. The writer rangle : Am. Jour. Sci., 5th ser., vol. 24, pp. 293-298, If32. GEOLOGIC STRUCTURE 73 overridden Paleozoic rocks. The northwestern part of cause the major anticlines and synclines in the Paleozoic the Martic overthrust block is covered by Triassic rocks rocks and in the Glenarm series of the Hanover-York from 7 miles southwest of the Hanover-York district district are parallel to the late Paleozoic folds of the to a point east of the northeast end of the Frederick Appalachian Valley to the northwest, the foldirg in Valley. From that point southward across Maryland, both areas is probably of the same age. This folding was the Ijamsville phyllite 33 largely of tuffaceous origin, later than the recumbent folding and formation of folia forms the western border of the Martic overthrust and tion layers that were developed during or before the for is in contact with Lower Cambrian Antietam quartzite ward movement of the Martic overthrust block. No and Upper Cambrian Frederick limestone. On Mo- evidence has been found to show whether the overt!: rust nocacy Eiver, 7 miles south of Frederick, a contact of ing of the Martic block and the latter folding took place Ijamsville phyllite and Frederick limestone is exposed during two stages of late Paleozoic orogeny, or whether on the south side of the River. This contact surface the Martic overthrusting and recumbent folding took dips 55° SE. The fold axes in the Ijamsville phyllite place in an earlier orogeny. also dip 55° SE. The folds are in large part sheared TRIASSIC STRUCTURE out by cleavage parallel to the axial planes, which dip 75° SE. Tension joints healed by quartz cut cross the STRUCTURAL FEATURES OF THE TRIASSIC ROOKS fold axes. The dip of the cleavage in the Frederick The Triassic rocks that cover the northwest third of limestone at the contact is 55° SE., and on the cleavage the Hanover quadrangle are not folded, as are the older faces are linear streaks parallel to the lineation and fold rocks to the southeast; but they are gently tilted north axes of the phyllite. The fold axes of the limestone are westward at an average angle of 30°, and in places are horizontal and strike N. 35° E., parallel to the contact. displaced by normal dip faults. In the adjacent region, The structural discordance of the phyllite and lime normal strike faults occur within these red beds, but no stone at the contact is obvious. In the Ijamsville strike faults have been observed in the Triassic rocks of phyllite and associated flows and marble that form the the Hanover quadrangle. The Triassic rocks are part western border of the Martic overthrust in Frederick of a great block that has been faulted down at its r orth- County, Md., the folds have steep axes,34 a type of western margin, 10 miles northwest of the Hanover structure that is confined to these rocks and does not quadrangle. During the faulting all the Triassic crocks occur in the limestones of Frederick Valley to the in the block were tilted northwestward. The major west. The folds are in part sheared out by transverse part of this faulting and tilting, therefore, probaWy oc cleavage and are compressed at right angles to the curred at or near the close of the Triassic period, when border of the thrust. conditions were favorable for the formation of normal Folds with steep axes are supposed to have developed faults, the sinking and tilting of blocks, and the intru in response to a check 35 of forward movement; but the sion of diabase into the sedimentary rocks through the compression and shearing out of the folds took place openings made by faulting in the floor of the basir. during a later stage of the orogeny when the linear South of Abbottstown two converging dip faults unite, streaking was imposed on the cleavage of the Frederick and the base of the northwestward-dipping Triassic limestone. The dip of the contact 55° SE indicates a rocks is offset more than half a mile. The basal con rather steeply-dipping thrust plane at this point and glomerate east of Beaver Creek School is offset rorth- probably elsewhere on the fault, which extends along ward to the road east of Walnut Grove School. Out the entire eastern side of Frederick Valley. crops of slickensided and crushed conglomerate along this fault can be seen on the highway (State 190). Two AGE OF THE STRUCTURAL FEATURES other dip faults offset the base of the Triassic series The rocks of the Martic overthrust block rest on Cone- just west of La Bott. The combined horizontal dis stoga limestone of probable Ordovician age. The date of placement here is also about one-half mile. Jus4: east the overthrust, therefore, is post-Conestoga. The Cone- of Paradise Creek, the conglomerate bed, slicker sided stoga limestone is correlated with limestones containing by the fault movement, is exposed along the road extend Beekmantown fossils in Chester Valley,36 hence, the ing northeastward from Farmers. A pebble of milky thrust fault is probably of post-Beekmantown age. Be- white quartz, cut in two and polished by the fault move ment, is shown in plate 15, C. ^Jonas, A. I., and Stose, G. W., New formation names used on the geologic map of Frederick County, Maryland: Washington Acad. Sci. TRANSVERSE FAULTS IN THE PALEOZOIC ROCKS Proc., Tol. 28, p. 346-347, 1938; Geologic map of Frederick County, Maryland, Maryland Geol. Surv., 1938. Several transverse faults that cut the Paleozoic rocks 84 Jonas, A. I., op. cit. (Am. Jour. Sci., 5th ser., vol. 34), pp. 376-385, trend, in general, N. 30° W. They terminate in normal 1937. 85 Idem., p. 385. strike faults that trend N. 50° to 60° E. Intersection 88 Stose, G. W., and Jonas, A. I., Age reclassiflcation of the Frederick of the two sets of faults tends to produce a rhombic fault Valley (Maryland) limestone: Geol. Soc. Amer. Bull., vol. 47, pp. 1671-1673, 1936. pattern. (See fig. 28.) 462857—44- -6 74 GEOLOGY OF THE HANOVER-YORK DISTRICT, PA. A cross fault that strikes about N. 30° W. cuts the plication due to the presence of a strike fault, obscure end of the Mount Zion anticline, crosses the limestone the direction of movement on the fault. Farther north lowland east of York, and follows Mill Creek to Plank the Highmount overthrust is offset northward on the Road, and hence is called the Plank Road fault. It west side of the cross fault, similar to the offset of the offsets the Sterner overthrust a quarter of a mile, the west Stoner overthrust. The cross fault terminates at the side having moved relatively northward. The Antie- Glades overthrust. tam quartzite and higher formations on the south limb A nearly parallel cross fault follows the local course of the Wrightsville syncline, just north of the Stoner of East Branch of Codorus Creek southeast of West 77*00' 76'4-S' FIGURE 28.—Map of normal tension faults in the Hanover quadrangle and adjacent part of tbe York quadrangle. D, downthro^vn side. Arrow shows direction of relative horizontal movement. Observed relation of faults to Triassic rocks shown. Faults marked P apparently affect only the Highmount thrust block and are believed to be of late Paleozoic age. overthrust, are similarly offset. To the south in the York, and passes near the York Country Club, and is, gorge of Mill Creek, the quartzite beds in the Chicldes therefore, called the Country Club fault. It offsets the slate and the infolded Harpers phyllite are broken and Stoner overthrust northward on the east side. South of offset in the same direction. The relative horizontal this overthrust, Harpers phyllite west of the cross fault movement on this part of the fault is therefore the west is in contact with Chickies slate to the east. In the lime side moved northward. On the north limb of the stone of the valley north of the Stoner overthrust, an Wrightsville syncline, the Kinzers formation and Vin anticline that brings up Kinzers formation and Vintage tage dolomite east of the cross fault are terminated dolomite is cut in two; but the parts of the fold do not abruptly by the fault, but the absence of exposures in match. Evidence of the direction of movemert on this the Mill Creek lowland west of the fault and the corn- fault, therefore, is conflicting. The Country Club fault GEOLOGIC HISTORY 75 terminates at the north in the Graybill fault, which is the structural features of the Pigeon Hills and .offset apparently a normal strike fault downthrown to the the Stoner and Gnatstown overthrusts. Some of them south. The Country Club and the Plank Koad cross also cut and offset the Triassic beds and, therefore, in faults appear to end at the south in another strike fault, part at least, are of Triassic age. It is probable th? t the the Keynolds Mill fault, which also is downthrown to faulting and adjusting of blocks took place under condi the south. tions of tension at the beginning of the Triassic period, Several nearly parallel cross faults, marked P in figure during the formation of the basin in which the Tr:assic 28, break up the rocks in the Highmount overthrust sediments were later deposited. Many places along the northwest of York but do not pass into the overridden northwest border of the Triassic rocks show evider ce of limestone. These faults apparently represent part of such early Triassic faulting during the formation of this the fragmentation of this thin plate during overthrust- basin and its progressive sinking. ing, as described under Mount Zion anticline, and, there fore, are believed to be of Paleozoic age. GEOLOGIC HISTORY The Pigeon Hills anticlinorium is cut almost at right angles by several transverse faults. Near the west end The geologic record is plainer in the northern and of the anticlinorium two nearly parallel faults, the central parts than in the southern part of the Hanover- Beaver Creek School faults, converge and join to the York district; and for this reason the two parts are northward. These faults not only offset the structures described separately. in the older rocks but extend into and offset the Triassic In later pre-Cambrian time the northern part of the rocks to the north and, therefore, in part at least, are of district was receiving outpourings of both basaltic and Triassic age. Two other cross faults, which terminate rhyolitio lavas. The exposures of these lava floras in the north arm of the High Kock anticline, also cut and this area are small, but observations farther to the offset the Triassic rocks between Farmers and La Bott southwest indicate that contemporaneous volcanic flows, and, therefore, at least in part, are also of Triassic age. mixed with ash, breccias, and clastic debris, were wide The Iron Kidge cross fault, which trends about N. 30° spread. The volcanic rocks were spread over an older W., breaks across and offsets the folds of the Pigeon pre-Cambrian crystalline injection complex, whi°-h is Hills anticlinorium near Gnatstown, (See pi. 17 and now hidden in this area but is exposed northeast of the fig. 28.) At Iron Ridge it offsets the Stoner overthrust Susquehanna River. There, volcanic rocks either were northward on the west side. This fault terminates at never present or were removed by erosion before the the north in a northeastward-trending normal fault basal sediments of Lower Cambrian age were deposited within the High Rock anticline. A shorter parallel cross on the earlier injection complex. The pre-Cambrian fault, one mile to the west, also cuts the Pigeon Hills injection complex in adjoining areas was composed anticlinorium, apparently breaks the northeastward- originally of sandstone, shale, and limestone that were trending normal fault referred to previously, and at the later intruded by gabbro, folded, permeated with ma south terminates in another northeastward-trending nor terial from granitic magma, and metamorphosed into mal fault. A cross fault that trends more to the north schists and gneisses during the intrusion of large masses west cuts off the southwest end of the Gnatstown anti of igneous rock. Residual liquids of the intruding cline and terminates at the north in the east branch of magmas formed pegmatite veins, which cut the layered the Beaver Creek School fault. Southeastward this fault gneisses formed earlier. The resultant injection com crosses the limestone lowland, and offsets the Stoner plex covered a wide area in the Appalachian region in overthrust at Smiths Station. It is therefore called the pre-Cambrian time, and was intensely folded and eroded Smiths Station fault. The thin remnant of the Stoner before the later volcanic flows were poured out. The overthrust block is considerably dissected east of this only clue to the age of the intrusive igneous rocks that fault, and in the vicinity of Smiths Station the east form such a large part of the old complex comes from side seems to be relatively uplifted to such an extent the pegmatites in Pennsylvania and Virginia. Analyses that erosion has removed the rocks above the overthrust of radioactive minerals indicate that the pegmatites and produced the large embayment at Penn Grove. were formed over 800 million years ago. The volcanic rocks are much younger and probably represent the- last AGE OP THE TRANSVERSE FAULTS stage of pre-Cambrian history. The Country Club and Plank road cross faults cut and Following the extrusion of the lavas, the land was offset the Stoner and Highmount overthrusts and other elevated and eroded before the region was submerged structural features of the area. They and the associated in Lower Cambrian time. Clastic debris was then normal strike faults, therefore, are younger than these washed into the sea by streams from an old land area structural features, and may be partly, or wholly of to the southeast. The first sediments were largely un- Triassic age. The Iron Ridge, Smiths Station-, Beaver sorted quartz sand, feldspar grains, clay, and coorser Creek School, and other cross faults similarly cut across round pebbles of milky and glassy quartz. These de- 76 GEOLOGY OF THE HA1TOVEIR-YOEE: DISTRICT, PA. posits are now represented by the Hellam conglomerate Conestoga time the sea invaded an irregular land surface member of the Chickies quartzite. The coarse cobbles on which there were large and small blocks of white found in the Hellam conglomerate in the vicinity of the marble residual from the older formations These Hellam Hills may indicate a local shoaling of the sea fragments were transported only a short distance from at this point while off-shore material was being contrib their source and were engulfed in the calcareous silt of uted elsewhere. Following these early sediments, the Conestoga. The white marble blocks contain no purer, well-sorted quartzose sands of the Chickies fossils but resemble beds of the Kinzers formation. The quartzite were deposited. Some distance southeast of old land surface furnished white quartz sand, which was the Hellam Hills area, clayey mud and some quartz sand carried by streams, or blown by the wind, into the sea of the Chickies slate was being deposited at this time. and incorporated in the early calcareous mud deposits. Fine clay and silt, now represented by the Harpers phyl- Consequently, limestone containing abundant rounded lite, collected in the sea before a closing stage of the quartz grains is a characteristic part of the lower beds terriginous deposition, furnished the quartz sand of the of the Conestoga. The sea was of variable depth; and Antietam quartzite. The presence of life is not re in places, wave action broke the recently formed layers corded in the lower beds of the Cambrian system; but into tabular blocks, which came to rest at varying angles the borings of sea worms, Scolithus linearis, are numer in the calcareous ooze and were consolidated into the ous in the massive beds of the Chickies and Antietam edgewise and intraformational conglomerates that are quartzites, and trilobites and brachiopods, which lived interbedded with the argillaceous and siliceous lime along the shore of this sea, are preserved in the upper stones of the Conestoga. Intraformational and edge layers of the Antietam quartzite. About 2,500 feet of wise conglomerates are most plentiful in the lower part quartzose and clayey material was deposited in the of the formation. The alternate accumulation of fine Lower Cambrian sea before the waters cleared and car calcareous silt and argillaceous silt, containing a vari bonate sediments, derived from the sea water by precipi able quantity of carbonaceous material, continued after tation aided by organic life, together with small amounts the basal conglomerate was formed, and the larger part of clastic material, were deposited. These sediments of the formation is composed of these impure limestones. formed the Vintage dolomite, followed in this area by a There is no record that Paleozoic sediments were de series of impure carbonate, clayey, and sandy beds of posited in this district after Conestoga time. Farther the Kinzers formation.- Trilobites and brachiopods northwest, sediments were deposited during the re were abundant in the sea at this time and are more mainder of Paleozoic time, and they aggregate many numerous and better preserved in the rocks of the Kin thousand feet in thickness. The formations in the Val zers formation than in the earlier carbonate rocks. The ley and Ridge province represent these later rocks. purer limestone beds of the Kinzers contain reefs of Before discussing the period of folding and mountain archaeocyathids which are probably fossil sponges. building that affected the entire Appalachian region While the clayey and limy silts of the Kinzers formation at the close of Paleozoic time, the geologic history of the were being deposited in this part of the sea, purer southern part of the district will be described. The carbonate sediments accumulated continuously in the Glenarm series was deposited in a basin that lay some Lower Cambrian farther to the northwest. Pure lime distance to the southeast of the present position of these silt, which followed the impure beds, eventually became rocks. The floor of the depositional basin is not seen in the Ledger dolomite. The Lower Cambrian carbonate this district; but farther to the southeast near the south rocks may have been deposited as calcium carbonate, eastern border of the Piedmont Plateau, the floor is and their partial or complete change to dolomite may exposed in several upfolds. This basement is formed have occurred at a somewhat later time. by pre-Cambrian Baltimore gneiss and Hartley augen Carbonate sediments were deposited during the rest gneiss. These gneisses resemble those of the floor on of Cambrian time in adjacent regions, but no traces wliich the later pre-Cambrian lava flows of th?- Hellam of these rocks are known to be preserved in the Hanover- Hills and Pigeon Hills are believed to have been ex York district unless the Conestoga limestone is in part truded. The source of the sediments of the Glenarm of Upper Cambrian age. The region was uplifted and series was a land area still farther to the southeast in stood above sea level in late Cambrian or early Ordovi- the region now covered by the sediments of the Coastal cian time, and some of the recently deposited sediments Plain. were eroded from the land before it was resubmerged The earliest sediments deposited in this southern sea and the Conestoga limestone was deposited. In the were arkoses, finer arkosic and quartz sands, r.nd argil Hanover-York Valley, the Conestoga limestone lies on laceous muds. After the accumulation of the felds- Ledger dolomite and Kinzers formation; but south of pathic sand and silt, rather pure calcareous material was the Stoner overthrust, it overlaps on the Antietam deposited and was followed in the southeastern part quartzite, with the Vintage dolomite and Kinzers for of the sea by a thick series of arenaceous and argillaceous mation exposed in a few places. At the beginning of sediments. This phase of the Glenarm series, which GEOLOGIC HISTORY 77 has been metamorphosed into the Setters formation, the and Pigeon Hills anticlines farther northwestward. Ir Cockeysville marble, and oligoclase-mica schist facies places the folded and overthrust rocks are broken by of the Wissahickon formation, together with the under normal faults, some of which represent the last stages of lying Baltimore gneiss, is now exposed to the southeast this deformation. of the Hanover-York district. In the northwestern part After the Appalachian orogeny, the elevated regior of this southern basin, volcanic activity began during was eroded until the Triassic period, when an elongated the formation of the calcareous sediments. The vol basin was formed in the upland surface by downwarp- canic deposits were in part submarine because the rhyo- ing and by normal faulting chiefly at the west edge of lite and basalt flows were mixed with volcanic ash and the area. The trend of the basin in part parallels the quartzose terriginous sediments. Volcanic materials, older structures and in part cuts across them in a more mostly pyroclastic, continued to be deposited and are northerly direction. The red sands and clays of the interbedded with the later accumulation of coarse and Newark group, which was deposited in this basin, were fine clastic siliceous material. These sediments are now derived from higher land to the southeast. The crystal represented by the Wakefield marble, which may be con line rocks on this upland were deeply weathered and dis temporaneous with the Cockeysville marble; metabasalt integrated, and furnished the quartz and the feldspathic flows; rhyolite flows, and tuffs, including the Urbaua sand, the clay, the flakes of mica, and the red iron oxide, and Ijamsville phyllites most widely distributed in which accumulated in the basin to a great thickness Maryland; the albite-chlorite schist facies of the Wissa Downfaulting and progressive sinking at the northwest hickon formation; and the Marburg schist and associated edge of the basin caused the ovelapping of beds towarc1 quartzites. In the southeastern part of the area, south the western part of the area and tilted the beds rather east of the York-Hanover district, the Glenarm series uniformly northwestward. Toward the close of Trias was later intruded by igneous rocks which range in com sic deposition, the great fault break in the floor near the position from granite, through granodiorite, diorite, west edge of the basin offered a means of escape for and gabbro to serpentine and pyroxenite. basaltic magma. The lava welled up also along ver The deposition of the Glenarm series and the igneous tical joints in the Triassic rocks, and hardened into activity that followed were completed before Cincin- diabase dikes. The larger part of the magma was in natian time. The rocks of the Glenarm series were jected between layers of the sedimentary rocks anc1 later greatly metamorphosed and closely folded. The hardened as great sills of diabase, such as the one ir present position of the rocks of the Glenarm series upon the northwest corner of the Hanover quadrangle. Heat, the Paleozoic rdcks to the northwest is the result of and hot water from the intruded diabase baked the ad overthrusting, which occurred after the deposition of joining Triassic sedimentary layers and changed their the Coiiestoga limestone in Ordovicion (?) time. The color from red to dark gray or bluish black. Some of small scale recumbent folds seen in the rocks of the the smaller dikes that came up through the Paleozoic Glenarm series suggest large scale recumbent folding and pre-Cambrian rocks beneath or south of the Triassic during the northwestward movement of these rocks sediments extend entirely across the district to the along the Martic overthrust. Although the rocks of the Maryland State line.' Glenarm series cannot be definitely dated, their deposi At the close of Triassic time, further movement or tion and accompanying volcanic activity probably oc the faults at the west edge of the Triassic basin tiltec1 curred late in pre-Cambriart time. the Triassic rocks still more so that now they all dip The main overthrusting probably began early in the toward the northwest edge of the basin where they ter period of compression and mountain making that took minate against a marginal chain of normal faults. The place at the close of the Paleozoic era, when the rocks Triassic rocks in this area were also broken by vertical of the Hanover-York district and the entire Appala dip faults, which in places offset the beds and their basal chian region were closely folded and raised above sea boundary about half a mile. level. Since Triassic time the district has been continuously Metamorphism, which began in the rocks of the Mar- above the. sea. Except alluvium along the larger tic overthrust block during recumbent folding and streams, no sediments have been deposited but on the thrusting, continued in both the overthrust rocks and contrary, the land has been extensively eroded. At the- the overridden Paleozoic rocks during the late Paleo beginning of Cretaceous time, all the rocks, including zoic deformation that compressed both series into folds the hardest and most resistant, were worn down to $. with northeastward trends parallel to the trends in the nearly level, gently rolling surface near sea level, form main Appalachian region to the northwest. Many of ing the Schooley peneplain. During Tertiary time thir these folds are overturned toward the northwest and surface was raised and again was subjected to erosion, are broken by thrust faults along which the rocks moved Remnants of the Schooley peneplain are preserved in the northwestward. This folding and overthrusting moved Pigeon Hills at an altitude of 1,140 feet and, in the the rocks of the Stoner block and of the Hellam Hills southern part of the district, at about 1,000 feet. The 78 GEOLOGY OF THE HANOVEIR-YORK DISTRICT, PA. / rolling upland in the southern part of the York quad part of the Hanover quadrangle, range in altitude from rangle attains a rather uniform level, mostly ranging 520 to 560 feet and probably represent the Harrisburg from about 900 to 1,020 feet in altitude with a few peneplain. The limestone in the flat lowland around points 20 to 40 feet higher. This flat upland surface Hanover is deeply weathered and has almost no out is best shown at Shrewsbury, Mt Airy School, Mt. Olivet crops, indicating long exposure to the agerts of weath Church, and the hilltop southeast of Winterstown. The ering and little reduction of level by erosior. This low flat top of this hill is 1,020 feet in altitude and covers land, which is from 600 to 620 feet in altitude and forms nearly half a square mile. The flat hilltop in the vicinity the divide between streams that flow eastward into the of Mt. Olivet Church is from 1,000 to 1,020 feet in alti Codorus and westward into the South Branch of the tude and extends in a northerly direction almost contin Conewago, probably also represents the Harrisburg uously for more than two miles. Smaller flat uplands peneplain. are at the same general level on Rocky Ridge, Dug Hill The present mountains, valleys, and lowland have and its extension southwest of Sticks, and the hills in been sculptured out of the rocks in these uplifted the northern part of the Wentz syncline southwest of surfaces. Beecher Hill. These flat surfaces at approximately 1,000 MINERAL RESOURCES feet altitude probably represent the Schooley peneplain, The chief mineral resource of the Hanover-York and the writers believe that these levels have been little district is limestone, which is extensively quarried for reduced by erosion since they were formed. Flat hill lime burning, cement manufacture, and crushed stone. tops that stand about 900 feet above sea level, however, Iron ore was mined formerly to a considerable extent, may have been reduced 100 feet or more by erosion. but none of the mines are being worked at present. Ashley 37 believes that these mature elevated surfaces Sand and clay are dug locally for building purposes have been greatly reduced since their formation by and for brick manufacture. Slate has been prospected erosion and weathering, possibly at the rate of 1 foot at several places, but none has proved of suitable quality in 10,000 years, but that the remnants still preserve their for roofing purposes. Red Triassic sandstone, Lower level character. The writers do not agree with this view.38 Cambrian quartzite, and in the southeastern part of the area quartzite, metabasalt, and mica schist are used The Pigeon Hills, 10 miles north of the hills of the locally in building dams, bridge piers, walls, and stone Wentz syncline, rise to altitudes of 1,000 to 1,240 feet. fences. The descriptions of quarries that follow present The Schooley peneplain is probably here represented by the conditions that existed in 1937 or earlier. a rather flat bench at 1,140 feet, which is 120 feet higher than the Schooley level 10 miles to the southeast in the HIGH-CALCIUM LIMESTONE southern part of the district. Two rocky peaks that rise Limestone of unusual purity occurs ir the middle above this bench are probably monadnocks on the member of the Kinzers formation. In mo^t places this Schooley peneplain. In this district the Schooley sur pure, high-calcium rock is too thin to be cmarried on a face, therefore, slopes about 120 feet in 10 miles, or Jarge scale; but in the York Valley, from York to 12 feet to the mile. Flat tops of ridges in South Moun Thomasville, it attains a thickness of 100 feet or more tain, Adams County, 20 to 25 miles northwest of the and has been extensively quarried. Many old quarries Pigeon Hills, rise to an altitude of about 1,600 feet but were located in and around the city of York, but most are less extensive than the broad flat top of South Moun of them have ceased operation. This pure limestone tain, called Big Flat, whose altitude is 2,050 feet. This is now actively quarried in the Hanover-York district flat surface is regarded by the writers as a remnant of by 4 companies; and similar high-grade rock probably the Schooley peneplain. The marked discrepancy of this level with that of the Schooley peneplain on the underlies much of the area mapped as the middle mem Pigeon Hills and in the area to the southeast, has been ber of the Kinzers formation northwest and west of explained by Stose 39 as due to post-Cretaceous faulting. York and in the vicinity of Thomasville. For a de By the close of Tertiary time, the softer rocks at the tailed description of the limestone quarries in the area, surface were again reduced by erosion to a gently slop as well as the technology of the industry, the reader is ing, nearly level plain, and remnants of this surface, referred to Miller's comprehensive report * } on the lime called the Harrisburg peneplain, are preserved at alti stones of the State. The product is used for whiting, tudes ranging from 620 to 520 feet. The flat-topped portland cement, flux in the steel and glass industries, hills of Triassic sandstone and shale in the northwestern and, either raw or burned, for agricultural lime. The Palmer Lime and Cement Co. plant, now oper * Ashley, Geo. H., Weathering and erosion as time markers (abstract) : ated by the Universal Gypsum & Lime Co., is in the Geological Soc. America Proc. for 1937, p. 70, 1938. southern part of West York, on a branch line of the 38 Stose, G. W.. Age of the Schooley peneplain : Am. .Tour. Rci., 5th ser.. vol. 238, pp. 461-470, 1940. 89 Stose, G. W., Possible post-Cretaceous faulting in the Appalachians : 40 Miller, B. L., Limestones of Pennsylvania: Pennsylvania Geol. Sur Geological Soc. America Bull., vol. 38, pp. 493-504, 1927. vey, 4th ser., Bull. M 20, pp. 9-112, 702-712, 1934. MINERAL RESOURCES 79 Pennsylvania Railroad. Sketches of the active quarries the Western Maryland Railroad. The rock is a high- of the company, as well as several abandoned pits, and calcium gray to white marble of the Kinzers formation. details ^f structures exposed in the quarries are given The quarry is about 300 feet in diameter and has a 40- in figures 11 to 13. The rock in the large quarry ranges foot face. A concrete tower and storage bins and the from a compact dark impure limestone mottled with crushing plant are reached by an inclined tram. The dolomite at the base, said to contain 28 percent MgCO3, crushed rock is conveyed to the cement mill at West through a purer white marble mottled with gray, said to York, where Medusa white and gray portland cements contain 18 percent MgCO3, to a still purer compact are produced in a long rotary kiln. The product is white marble, which grades upward into gray mottled stored at the mill in two large vertical concrete bins. or spotted "calico rock," of higher magnesium content at the top. The high-grade rock is reported to contain IMPURE LIMESTONE from 98 to 99 percent CaCO3. The large quarry south Limestone and dolomite are burned for lime or of the plant is about 1,000 feet long by 600 feet across ground and pulverized raw for agricultural use. Im and has a 50-foot face. Kadiating tracks converge to pure limestone and dolomite are crushed for road the inclined tram that leads to the crushing plant north material and concrete. Small abandoned quarries, of the quarry where 2 crushing and pulverizing mills from which limestone was obtained formerly and and 10 vertical steel kilns are located. The new quarry burned for local use, occur throughout the area where to the northeast is connected with the old quarry by limestone is exposed; and similar rock is available for tunnels under the roadway, and tunnels also follow the these purposes in areas mapped as limestone. Only the high-grade rock beneath the plant. The high-grade larger active quarries will be described. rock is carefully hand picked, and some is burned for lime and some is crushed and pulverized raw for The York Valley Lime and Stone Co. quarry, now shipment. inactive, is adjacent to the Lincoln Highway north of The Thomasville Stone & Lime Co. has a large quarry Campbell. (See fig. 14.) A narrow gage track extends and plant half a mile south of Thomasville, on the West south from the quarry to the Pennsylvania Railroad. ern Maryland Railroad. The quarry is about 1,000 feet The rock is largely limestone conglomerate and impure long and its semicircular face is about 50 feet high. The slaty limestone of the middle part of the Kinzers forma limestone beds are nearly horizontal and have been tested tion and was used chiefly for crushed stone for highway by drill to a depth of 200 feet. The rock in the quarry construction. An inclined steel-car cable-tram leads is a high-calcium limestone, and rock of the same quality from the radial tracks in the quarry to a crushing plant is reported to extend to a depth of 100 to 150 feet below with elevated concrete bins above the tracks. A steam the floor. A shipment of 40 carloads of crushed rock shovel was used for stripping. Steam drills were used was reported to average over 98 percent CaCO3, and in the quarry, and the company had two well-drilling 10 carloads shipped to the Midvale Iron & Steel Co. rigs. The product was shipped by rail and motortruck. were reported to have averaged 99.69 percent CaCO3. Formerly, the purer rock was burned for lime in 12 Some of the rock is burned for lime and some is granu kilns located south of the highway, but these have not lated and pulverized raw for steel and glass plants. The been in use for several years. The quarry was operated less pure rock is crushed for road material. The equip for a time by the U. S. Gypsum Co. but was idle in ment consists of 2 well-drilling rigs, 1 stripping shovel, 1937. 3 loading shovels, 14 vertical steel kilns, and crushing The Eli Zinn Co. operates two quarries in the area and pulverizing plants. Radial tracks converge toward for crushed stone. Their largest quarry is in the im the inclined tram running to the crushing plant. pure dark-blue slaty limestone of the upper part of the The J. E. Baker Co. has a large quarry and plant just Kinzers formation on the south side of Highland Park south of Thomasville. An inclined tram runs to the Hill at Codorus Creek, south of York. (See fig. 16.). crushing plant. The company has another quarry north The quarry is about 200 feet long and has a face about of the Lincoln Highway at Thomasville, but it was 100 feet high. The other quarry is in the purer lime closed at the time of visit. This second quarry is also stone and marble of the middle part of the Kinzers equipped with inclined tram to the crushing plant. formation on the northeast slope of Greenmount Ceme High-grade rock is burned for lime in eight steel kilns, tery Hill. Both quarries are equipped with a crushing and some is pulverized raw. Less pure rock is crushed plant, screens, and storage bins; and the product is for road material. This company has a quarry also in hauled by motortruck. similar high-grade rock iy2 miles west of West YorV The York Stone & Supply Company has two quarries south of the Sandusky Cement Co. quarry. on the east face of Greenmount Cemetery Hill (fig. The Sandusky Cement Co., formerly the Medusa 10). The blue and white limestone of the Kinzers Portland Cement Co., has a large quarry and plant V/2 formation is crushed for road material. Sandy beds at miles west of West York and is reached by a spur from the top of the old, deeper quarry are fossiliferous. 80 GEOLOGY OF THE BOANOVEtR-YORK DISTRICT, PA. The Cunningham Crushed Stone Co. has a large Similar clay occurs in much of the area mapped as quarry in massive Ledger dolomite northeast of York, Conestoga limestone in the York-Wrightsville Valley. near Mill Creek, but it was idle in 1937 and is probably Several brick plants are located in the outskirts of abandoned. Sketches of a fault exposed in this quarry York. Two plants within the built-up part of the city, are given in figure 29. Across the road from this quarry are now abandoned. The Wm. H. Grothe Brick Co.'s the Standard Concrete Products Co. operates a quarry plant is southeast of the city, south of the East Prospect in banded limestone and dolomite of the Vintage forma road. Here a large area has been stripped, exposing tion. The rock is crushed and ground, and is used in closely folded hard impure crystalline Corostoga lime the manufacture of concrete building blocks. stone. (See pi. 7, B and G and fig. 19.) Some layers The A. M. Hake Co. formerly quarried stone in the of very impure schistose limestone are 20 feet thick and northeast part of York; but the extension of the city are deeply weathered to a sericitic clay which is the chief NW. SE. Standard CunrinSgham quarry ROAD quarry Pure limestone^ Dolomite (Ledger") xs (Vintage) J A o loo'Approx. SE. Fault breccia N and gouge ferruginous fault breccia 1" black clay 3'fault gouge breccia Ledger dolomite FIGOHB 29.—Sketches of faults m quarries northeast of York: A, Gen eralized cross section through quarries of Standard Concrete Products Co. and Cunningham Crushed Stone Co.; B and C, Sketch of plan and cross section of Cunningham quarry in 1921, showing detail of struc ture near the fault contact and accompanying breccia and gouge; D, Sketch of plan of present Cunningham quarry, showing detail of structure at fault. Trilobites were collected at point marked F. has encroached on the quarry and it was abandoned. source of the clay used. The plant consists of a long (See fig. 15.) The deep hole of the old quarry, is now drying shed and three Dutch kilns. filled with water and used as a dump for rubbish. The Spring Garden Brick Plant, east of York on The Koy Bittinger Co. has a quarry for crushed stone the Maryland and Pennsylvania Kailroad, also is in in the southwest part of Spring Grove adjacent to disintegrated argillaceous Conestoga limestone. The Codorus Creek. The rock is the thin-bedded crystalline plant is equipped with six beehive kilns and a long dry blue limestone with argillaceous banding and the mas ing shed. The chief product is a high-grade building sive impure limestone of the Kinzers formation. brick of pleasing color, called colonial brick. Sketches of faults and other structures exposed in this Brick made from ground slate was formerly produced quarry are given in figure 18. Trilobites were obtained 1 mile southeast of Spring Plains. The q-iarry was in from the thin-bedded crystalline limestone in this Chickies slate in the hills south of the plant, and was quarry. reached by a tram road which connected with the Penn BBICK CLAY sylvania Kailroad east of Spring Plains. The deep In the Hanover-York district, bricks are made from quarry is now filled with water, and tfce plant and the residual clay from impure limestone and from railroad track are dismantled. South of Hanover1, ground shale and slate. The impure Conestoga lime brick was made from the residual soil of shale of the stone yields the thickest deposit of clay and has fur Kinzers formation. The pit was 400 feet long and 1-5 feet nished the material used in the plants around York. deep. This plant is dismantled and the pit abandoned. MINERAL .RESOURCES 81 The Peerless Brick Co. has a plant on Codorus Creek for desultory hand screening of loose material. This north of York, just below the Elmer King sand quarry. pit is in the same beds as those more extensively ex The white sand from the quarry is mixed with clay ploited in the Conestoga limestone near McSherrystown from other sources, and a smooth white compressed in the adjacent Gettysburg quadrangle.41 brick is made. A lime-sand brick is also produced. The plant was not in operation at time of visit in 1936. SLATE Slate has been prospected at several places in the area, BUILDING SAND but none of roofing quality has been found. One mile southwest of Kinney School in the Hanover quad Sand is obtained in the Hanover-York district chiefly rangle, a quarry 20 feet deep exposes black to gray from disintegrated quartzite and from the crushing of smooth-splitting slate at the top of the Marburg schist, harder quartzite. The Chickies quartzite in Mount Zion and some large thin slabs were quarried for flagstones. Hill and in the Pigeon Hills is the chief potential source Half a mile east of Zumbrum School, similar slate at of this sand. Some residual material is also obtained the top of the Marburg schist was prospected for roo.^ng from disintegrated sandy limestone. Such beds occur material. Black slate was quarried from the Chickies locally in the Conestoga limestone in the vicinity of just south of Plank Road, but the slate is too fiesile Hanover. for roofing purposes. Two slate quarries were opened The only active sand operations in the area are at by L. P. Litsinger of York on Kreutz Creek southwest of the quarries of Elmer B. King and Bro. and the Neuman Yorkana. In both quarries thin quartz layers are inter- Sand and Supply Co. in the gorge of Codorus Creek, bedded in the black slate. 2 miles north of York. Two quarries are opened in the Chickies quartzite above the Pennsylvania Railroad, STONE and the product is brought by gravity to the crushing Quartzite is quarried for building purposes in nr»ny plants at the railroad. The lower quarry is about 20 places in the area. The thinner-bedded rocks are sr>lit feet wide and has a 30-foot face. The upper, larger into slabs of suitable size for foundations, bridge piers, quarry has a length of about 300 feet into the hill and and walls. The Chickies quartzite is the chief source a 40-foot face. The rock is crumbly thin-bedded gray of such stone, and the geologic map shows the areas to purplish rusty-weathering quartzite, which contains of outcrop. some harder vitreous beds. The rock is crushed, Stone has been obtained at several quarries in the ground, and screened, and delivered to storage bins Chickies quartzite, on the south slope of the Pigeon Hills above the loading platform. The product is loaded north of Hanover. The two largest stone quarries in into cars and trucks by gravity the area are 2 miles west of Spring Grove. Similar Sand from disintegrated white arkosic quartzite of stone has been quarried in the Hellam member of the the Hellam member of the Chickies was obtained on Chickies quartzite on the south slope of Mount Zion Mount Zion Hill southeast of Pleasureville. The pit Hill, northeast of York. was operated by W. J. Herman, and considerable sand Stone is also obtained from quartzites in the Chickies was taken from a pit 12 feet deep. Disintegrated slate at two quarries near the York and Windsor Electric quartzite beds in the Chickies slate south of the York Railroad, 1 mile southeast of Violet Hill, and on Hill valley were quarried on the Dallastown Pike 2^ miles Creek near Benroy. Blocks are quarried for fourda- southeast of York. Clay also was obtained at this tions, and some rock is crushed for concrete and road quarry. Another old sand pit in this quartzite is on material. the top of Violet Hill 1 mile south of the reservoir south The quartzite at the top of the Marburg schist has of York. This pit exposes much crushed and brec- been quarried 1% and 2% miles southwest of Red Lion, ciated schistose quartzite, deeply stained with iron and and 1% miles southeast of Red Lion. It was also quar injected with quartz veins, which mark a fault zone. ried, probably for bridge piers, half a mile northwest Sand was dug from disintegrated quartzite at the top of Brodbeck. The Antietam quartzite has been quar of the Marburg schist 1% miles east of Ked Lion. Dis ried for building stone at localities 1 mile, 2 miles, and integrated Triassic diabase is a local source of sand on 3 miles south of Pennsville, in the western part of the State Highway 190 in the northwest corner of the Hanover quadrangle. It has been quarried also, prob Hanover quadrangle. ably for road material, near the head of West Branch TheHershey Sand Co. has a pit in disintegrated sandy of Codorus Creek southeast of Kreiitler School, and limestone in the northeastern part of Hanover, where near Cold Spring 1% miles northeast of Jefferson. highly sandy limestone beds in the Conestoga limestone Limestone has been used for building foundations, have disintegrated into a rough ferruginous sand, which bridge piers, walls, and stone fences; and in pioneer is dug and screened and used for building purposes. (See 41 Stose, G. W., Fairfield-Gettysburg folio, U. S. Geol. Survey Geol. pi. 8, A and B.) The quarry was inactive in 1936, except Atlas, folio (No. 225). p. 20, 1929. 462857—44———7 82 GEOLOGY OP THE HANOVER-YORK DISTRICT, PA. days, many houses were built of the limestone that was quartzites of the Chickies slate, Harpers phyllite, and quarried locally. Wissahickon formation and in the metabasalt. In Just south of Seitzland, metabasalt was quarried for places the magnetite is more concentrated, and residual bridge piers. masses of good magnetite ore may be found in fields IRON ORE adjacent to the outcrops of these rocks, but no ore of commercial value has been developed. A pit 1 mile Low-grade iron ore has been mined at many places north of Strickhausers, in ferruginous quartzite of the in the area, but none has been taken out for many years. Harpers phyllite, is the only place where magnetite is Most of the ore is residual limonite in the soil, and known to have been prospected in the area. thorough washing is required to remove the clay and quartz. The ore is not of commercial grade at the pres OIL AND GAS ent time. It is geologically significant, however, as many of the deposits are associated with limestone and Neither oil nor gas are to be expected from rocks in suggests its presence where not exposed. In narrow this area, but a well was drilled for oil on the top of a valleys, where deep weathering and solution have re hill east of York New Salem. The well was sunk on sulted in a thick soil cover and there are no rock ex an anticline of quartzite in the Chickies slate, north of posures, the presence of limestone is suggested by the the road running east and half a mile east of the cross iron ore. It also is commonly present along faults in roads. No oil was obtained and the well was abandoned. limestone, where circulating water has brought the iron to the surface and deposited it in the soil. WATEB SUPPLY The uppermost beds of the Antietam quartzite are The city of York requires a large quantity of water very ferruginous, and iron ore accumulates as float in for its population and extensive industries. A bountiful the soil overlying the Vintage dolomite at the foot of supply of pure, soft water is obtained from Codorus the dip slopes of hills composed of Antietam quartzite. Creek in the hills south of the city. A dam on the East Deposits of iron ore may be found, therefore, at most of Branch of Codorus Creek, 1 mile w^st of Jacobus, ponds the contacts of the Antietam quartzite and Vintage the large body of water called Lake William?, the upper dolomite shown on the geologic map. Extensive de end of which reaches to the highway (U. S. 111). The posits of this type have been mined on the borders of slopes of the hills surrounding the lake are protected the Antietam quartzite on the southeast side of the from soil erosion by a, dense growth of evergreens. The Pigeon Hills from southwest of Mt. Carmel School pumping and filtration plant is located farther down northeastward nearly to Nashville. Iron ore similarly East Branch. A distributing reservoir on Violet Hill, associated with the upper beds of the Antietam has been iy2 miles south of York, is more than 200 feet above mined also south of Jacobs Mills, 1% miles north and the city. V/2 miles west of Spring Grove, and 1 mile northwest Hanover has a reservoir at several large springs in a of Stonybrook. ravine on the south side of the Pigeon Hills 1 mile east Iron ore has been mined also where the Antietam of State Highway 194. This water supply was not quartzite is overlain by Conestoga limestone in the adequate for the growing industries of the city, and a Jefferson syncline from Jefferson northeastward to and larger quantity of soft water is now obtained from beyond Seven Valleys, in the syncline south of Mar- the Shepard Morris reservoir, 5 miles south of the city, garetta Furnace, in the East Prospect syncline west of where a dam, 1 mile southwest of Bandannr,, ponds the East Prospect, southwest of Klein School, south of Del- water of the South Branch of Conewago Creek. Ever roy, and in the syncline at Ore Valley. green trees were planted in 1937 on the slopes of the Some of the iron ore deposits may have been con hills in the vicinity of this reservoir. centrated by waters circulating along faults, especially Red Lion and Dallastown have a reservoir near the those near the Iron Bidge and Smiths Station cross headwaters of Cabin Creek, just below Locust Springs. faults. Ore pits are associated with faults at localities A small distributing reservoir is located on the hill south iy2 miles west of Mt. Carmel School, southeast of east of Dallastown. Spring Grove obtains its water Gnatstown, near Iron Bidge, at Hobart, and east of from Codorus Creek, which is ponded-southwest of the Nashville. Iron ore is associated with the Conestoga town. The Glatf elter paper mill in Spring Grove drilled limestone near the Stoner overthrust east of York Road several wells in the valley south of the town in 1936 and and in the valley at Penn Grove and south of Iron 1937 to obtain an adequate supply of pure, soft water, Ridge. Iron ore was formerly mined at the contact of and constructed a new reservoir just below the Hanover the Wakefield marble and the Marburg schist northeast road. of Loganville. Some of the small villages obtain their water from Crystals of magnetite up to an eighth of an inch in small reservoirs on nearby streams, but most of the diameter are scattered through some of the ferruginous smaller settlements depend on individual wells. INDEX Abstract_...__.._____._____.______.__ vii Farquhar Hill, features of—.....______...__——.——— 23 Accomac, section near...... _..___.______.....___..._...... 8 section on..______-.-.-.____..——.... ——————————.- 23,29 Acknowledgments-.______.._....__._.____.. 2 Faults, description of—...... —..—..60, 61, 62-64, 65-66, 73-75, pis. 5, D, 6, A, B Albite, origin of.____.______.______.______.___ 46-47 Fieldwork...-———.__——————————————.————— ——— 2 Albite porphyroblasts, relation of, to crystallization of schists.....___._._. 47-49 Fishing Creek, features of______- ___——__— 4 Alluvium, distribution of....__-_-______.______..___.__.. 59 Folds, recumbent, in the schists...______--.-._.——.--.- — ——.... 40,41 Ambau anticline, features of ______.______. ___. ___ 60 Foliation, definition of.—.______— ---——--...... - -41 Anticlines, descriptions of. —...... 10-12,13,59-62,64,66,57-68,70,71 in the rocks______.___..______:....__.——.._— 4i, 53 Antietam quartzite, building materials from..._...... _.___.—__—_.. 81 Fossils, lists of...... —————— ————————— —— — —— — —— — — 31,32 description of.____...... ______._...... 14-15, pi. 4 iron ore in...._____...... _....______..._...... __.... 82 Gas, prospects for__..__.——.. —. ——.——————...... — —... —..-_ 82 name of-______...... ______.___....______14 Geologic history of the area....—_._ — -._. —————— -————. — -——— 75-78 sections of.__...__...._.___..___...... ______15 Gettysburg Plain, features of...—__._....._ —. ———.... ————————.. 4 Arvonia slate, age of._._____...... _.___..__..-._...-..___._ 51,52 Gettysburg shale, description of..___...... —... ——.——————— 56, pi. 15, D Gettysburg sill, features of__.______...__------——.————————— 57,58 Baker, J. E., & Co., quarriesof-...- —...... - — . ——--.-.--... — .. 18,33,79 Glades overthrust, description of...—-___-.--.__---.._----_ ——— ——...-. 62 Beaver Creek School faults, features of.__.. _.______.__.____ 75 Glen Rock, population of.-..-——__.....----.---.-.-- — -... ——..-----. 1 Bittinger, Roy, Co., quarry of._____"..______.______30,31,80 Glen Rock anticline, description of._.---___....--_--._ —— —————.-.----. 70 Blue Ridge-Catoctin Mountain anticlinorium, structural relations of—- — -- — 5,64 Glenarm series, age and character of..-_-...----.---..- — — — -'-... —— -. 50-54 Brick clay, source of._...... _.______....._...... __.._. 80-81 deposition of beds forming——..-—....-„. ——..—————————————- 76-77 Brodbeck, section at__--...... -______.....______44 structural relations of.___-__„.._...——. —————————-——— 71-72 Building materials, sources of...... ______._____...... _____. 80-81 Gnatstown anticline and overthrust, description of-,...- ——————— -——.. 60,61 Greenmount Cemetery Hill, sections on..-.. — _ ——— _. ——————— — —— 28,30 Cambrian rocks, description of....______._____-_____ 4-5,6-34 Grothe, Wm. H., Brick Co., plantof...... —---.. — -——--—--—— 80 Cambrian time, events of_..._.______.______75-76 Cardiff conglomerate, age of...... ______..______._____ 52 Hake, A.M., Co., quarriesof—-.....------—_-- — -—------27,80 Catoctin Mountain-Blue Ridge anticlinorium, structural relations of.__ ___ 5,64 Hanover, population of.___.__.„-.-.-.------—— —...... ——..— 1 Chickies quartzite, building materials from..______.____.. 81 section near______.—. — --—.——— ———...- ——— --- 36 deposition of sand forming....______.______...___. 75-76 water supply for...___—__ ——._————————————— ——— — 82 description of. ______6-9, pis. 2, A, B, 18, A Hanover-York Valley, features of___...... —————————---_——--— 3-4 name of._.____...... ______..._____ 6 Harpers phyllite, deposition of beds forming-. — —.. — —— — ——— -——— 76 sections of._...... ___..__..__...__._.....__.... 8,9 description of.___.....—..—..—------13-14, pis. 3,18 B,C Chickies Rock, section near__.._.______._.______.. 8 magnetite in___.__._------_-._...-. — —— —— ..„-. —— -.__. 82 Chickies slate, building materials from______.___._..______80,81 name of______-...—--——.— —— ———. — —..- —— — -— 13 character and distribution of______...... 9-13, pi. 2, C, D Harpers shale, name of...... __--.. _.._ ——..— —————..----. — — 13 deposition of material forming....______...____.._____ 76 Harrisburg peneplain, geologic history of.—_-———_———— ——— — --... 78 magnetite in______.__.______.____.___...____ 82 Haycock sill, features of...-...__...____-...._— —————— ——... 57 sections of_.______...... __...... ___..._._._....______._ 11 Hellam, section at,.______.______.._.„.———-——————.— 30 Clay, brick from...__...... ______.___.___.______80-81 Hellam conglomerate member, building materials from....-. — -.——————- 81 Cleavage in rocks of area._._.._.______._____..._...... 11,35,36,43 character and distribution of.....-.-_---.-.--.--..-.--—- 7,8-9,12, pi. 2, A, B Clover Creek greenstone, origin of albite in______.___...... ____.. 47 deposition of...______...__._.-.-__--_----- —————..--. 75-76 Codorus Creek, features of______'.___..______....._____ 4 name of—_ ___-______.--....———————-—————————— 6 sections along____...... ______.___. —— __ —— — — 9,29 sections of..___..__...____...... _____ ————— — — —— 8,9 Columbia, sections near..__...... __.______._____ —______15,17 Hellam Hills, sections in—__'__.-_._.-_——___ ————-- —— - — — -- 8,15 Columbia granite, ageof.....___------.--.___...... _...... 51 Hellam Hills anticlinorium, features of—-___-____ —— _——. — -. — .- 61-62,64 Conestoga limestone, age and correlation of.___._.______.___ 37-38 Herman, W. J., sand pit operated by_ ——__...-.-.....-- —.-_... —.... 81 building material from.__.__...... ______.___ 80,81 Hershey Sand Co., pit of...___.______—- ——._ — — -_ —— — — — — — 81 character and distribution of..__.______.____ 34-37, pis. 7, 8, A, B, D High Rock anticline, description of.__..__——_ ———...... -- ——.— 7,60 deposition of._._._.___...... __.___...... ______..._ 76 Highmount overthrust, description of——__-----__ —— ——————— ---- 62-64 name of.___...... _.______._.____..._.___._...... 34 Holtz anticline, description of—. ______-__——-————————— 67-68 sections of--..--.---.--...... _..___-....._..-.--______..._..... 36 stratigraphic relations of.__..______34, 37, pi. 8, C Igneous rocks, age of-—.__....-.--..-..-..-.-----.----. —... —— - 6,53-54,75,77 Conewago Creek, features of_.______..__-_._...._.____._.-__ 4 character and distribution of————— — — -——- — — - 5-6, 56-58, pi. 16 Country Club fault, features of...... ______...... _._....______'74-75 Ireland, albite schists of.___.-..____...... _.--.-_ ——— - — — — 47 Cretaceous time, events of— —....--.._____._...... _..._..______._.. 77 Iron ore, character and occurrence of...------— — — — - ——— ——— -_..- 82 Cunningham Crushed Stone Co., quarry of_.__...... _..... 80 Iron Ridge fault, features of—...... _....._ — ——————— — ——...... 75 DaHastown, population of.._...... ___..__.....__...... ____ 1 Jefferson, population of-___.. water supply for_..____...... ______....__...... ______82 Jefferson syncline, description of. Dalradian series, origin of albite in...... ______..______47 Diabase, building materials from...... ______...__._.___.____..... 81 King, Elmer B., & Bro., quarry of..____._____.__ ..__------—— 81 character and distribution of.____.______...... ___.. 56-58 Kinzers formation, age and correlation of----_ — .„ — — -.-— — - ——— -- 30-33 Dikes, diabase, description of.____...______....._ 56, 57-58, pi. 16 character and distribution of-__. __ - _ ___. ___._ 18-30, pis. f, 6, C Dolomite, quarries in______....______.______.__ 22,24-26,33,79,80 deposition of__——.——.———————————————————————————— 76 Dolomite Products Co., quarry of_....______.__...... ______33 name of._ ———— — — ——__-——_------_..._------_——_-_._ 18 Drainage in the area______.______...... _...... ___. 2,4 quarries in______.______-__- ____-_._——— 78,79,8t> sections of-.————————————————— 19,20-21,23,24,27,28-29,30 East Prospect syncline, description of.....______....___.._.____ 67 Kline School, section near---.-..---. ——————.. ———————— -——————- 36 East York, sections in..__.__.______...______27 Kohlers Hill, section near_.—_.—————. — -——————-—————— 28 Emigsville, sections near.._...... _____...... __...... ____ 17,21 Kraft Mill anticline, description of-————————————————— 12,67 83 - 84 INDEX Page Laucks quarry, marble hu__-_---_____.______-__ —— __- — — .___. — .__.__ — 28 Saint Peters sill, features of..------— -—-- ———— —— 57,58 Ledger dolomite, deposition of—----__--___— .._ — _-_-_-_-_._--. — - — — 76 Sandusky Cement Co., quarry of------,------.--- —— — ———.. 79 description of.___.---__-_------___._----__ .-.--....-...__._. 33-34 Schooley peneplain, geologic history of— ------——————— 77-78 name of.._------__------_— -_-_- — _- — __- — ___ — - 33 Scotland, albite schists of__------__._ ————— -._-.. 47 quarriesin——----—————-——------—- — - —- — _ — -- 33,80 Shrewsburg, population of— — — ------...- — ------—— — — 1 Limestone, quarries in.——— — — — - — — — — — - — — - — ---.-. — -___.. 78-80 Sills, diabase; description of—~ —- — - — ------— — - — - —— ----- 56, 57, 58, pi. 16 Limonite, occurrence of — — ---_ — — _ — _-_--— — -_-- — - — _ — _—.__.— 82 Slate, building materials from___-_-______...__.... —...————————. 80,81 Litsinger, L. P., quarries of_------__---- — - — _—-__- —__.... 81 magnetite in_...... — _ — _ — --_-----..---.-.- — - —... - — — —— 13,82 Location of the area.-.-__------_...... __...... __... 1 Smiths Station fault, features of--.--- — ----- —— — ----— — ------——.—— 75 Loganville anticline, description of...... __.-.---_-_.__-_...... 71 South Mountain, metabasalt from_ — — -__.-_.______- — — -_ — — _ ————.— 6 Sprenkel School anticline, description of-___._-__ — — —— _ — — _-—— ---... 60-61 Magnetite, occurrence of ___———_-.-____-.__-. — _.„-._ ——— ___._._ 82 Spring Garden Brick Plant, features of_-___.---_...._.-----.-.--. —— —— --- 80 Marburg schist, building materials from______.- — - — - — ---...-.______.._ 81 Spring Grove, population of.--- — -- — —------——— ___-_-_ —. ————— „ 1 character and distribution of------42-43, 45-46, pis. 12, 13, A, B, 14, A, B section near ._-____.———__- — ---_-——_— — — __-- ———...—— 30 name of—-_ -______- —— ______..._— — — — — — —___ 42 water supply for..___...... —— — .-- — — -..—.... ———_————— 82 origin of— ... _._.. —— —————... ——...--. —-.---.—------50 Standard Concrete Products Co., operations by....----.-.------—... —— — 80 quartzites associated with-.--.----.------.--.------43-44, pis. 13, C, 14, C Stewartstown, population of-.-—--.--— — — - — -- — — ——- —— - — - —— - 1 Martic overthrust, age of.------_------73 Stoner, C. D., quarry operated by— — -—_-_-_ — __- — — — — — —— _.—... 37 description of------68,69 Stoner overthrust, description of._-.-- — -.-- — ...... ------. — --- —.... 64,65-67 evidence of....____._ — .- — -.---..... — — — ...-...--_...._.. 51,72,73 Stoner overthrust block, metamorphism in...-. ------— ---- 46 Martic overthrust block, rocks of._------____-_...---______._____— 5,38-54 Stoner quarry, section at..._.__- — - — ..-——....-_ —._. — — - ——.. 36 structural features of-___------__..-...-.-...... -._...... 68-73 Stonybrook dike, features of..—__.-.--..--.-- — --.„- —. — — __—__ — __ 57 Martinsburg shale, discussion of relation to Wissahickon schist.___...... 51-52 Strickler anticline, description of-__..._.-.---.---.-----.------.----_ 64 Medusa Portland Cement Co----- — —- —— - — -.-..------.-....--...... --.. 79 Structure of the area...... ____-..._...... _....._.. 59-75, pis. 1,17 Menges Mills anticline, features of...... --..---.....-. ...— —.___ .. 60 Sugarloaf Mountain, Md., rocks of, ageof..-.-.-_.____-~ —... —... 51 Metabasalt, analysis of——— — — .---_--__.-----______-...--_-_...--.- 6 Sykesville granite, structure of, relations of...... —.___._.____. 53-54 character and distribution of.__-_.___ — — ______-—-_,-_...... __ 5-6,39 Synclines, description of.------64,67,70-71 use of..-.-.--.__._._.———--_--.-- —-—-___ ———-______-_..- 82 Metamorphism, in the area.------_..--_...-. 13-14,15,44-49,58, pi. 15, A, B, C Terrace gravels, occurrence of-—------59 retrogressive, in the rocks.- —— __-_...... 45 Tertiary time, events of -___._.___...__---.-_-.____...- — .-.-.. — _- 77-78 MU1 Creek, section on.... — — _-...--. ——... —...... _..... 11 Thomasville Stone & Lime Co., quarry of-...-__-.___-----_____... 79 Mineral resources of the area_... —...... —....___...... 78-82 Topography of the area.—— — ___.-_-_-_-_-_.------.------_- —.. 4 Monnt Carmel School anticline, features of----.---- — —------60 Towns in the area----__._._._-_.------______-_._-____.... 1 Mount Pisgah anticline, description of----....---...-.. __...... _ 10-12,66-67 Transportation in the area__-...__------.-.---.-.---.-.-----__-.... 2 sections in-.____.-. — — — - — -- — — _—_...__-__...... __..__.....-... 11,15 Triassic rocks, description of- — _.___.—,_ — ... _____ — — 4-5,54-58,73, pi. -6 Mount Zion anticline, description of.___..---.------.--..__.-.----..-.. 61-62 Triassic time, events of------.------'----- — .--.------— ------Muddy Creek, features of--- — _-_-.-..-..--- — -- — ...--.___-—___ — — — 4 Tucquan anticline, description of-----.--- — -.-.------.-__..----..-.--.... 68, <0 Myers Mill, section near..—.. ——..._...... ___.__.__ 28 U. S. Gypsum Co., operations by._.----.._.-__...-.-______— ____._--__ 79 Neuman Sand & Supply Co., quarry of-_____- — — -—_---.— — _____...... 81 Universal Gypsum & Lime Co., quarries of--—------23-24,7£ 79 New Oxford formation, description of__...__-. — _ — -___-_-55-56, pi. 15, C Newark gronp, description of... — - — __.- —— -____ — -——._...._..... 54-56 Vintage dolomite, age and correlation of------_____------— — _____ 18 mode of deposition of material forming___,- — _ — — — ——..— —_.. 54 character and distribution of_-_____...______-___.... 16-17 North Midway, section in.-_—------_.....-____...--_.._..._...... 36 deposition of---.-_____-__.___...._____..._------___ 76 name of_.-.-.-.-...... ---.---.------.-.---.--__._._-_.------.---.-. 16 Oil, prospects for..- — _.-....--.----.....-.....-...... -----.---...-.-.-.... 82 sections of-----.------.------. — — -_- — — - — ---_— 17 Ordovician rocks, description of--_-..------.------.------...... _.. 34-38 quarry in.-_—--_.--_-_-_._._... —...... ——— — — _ — — - 80 Violet Hill, section near______-_— — — — — — _ — _--__._... 11 Paleozoic rocks, description of-_— —._____....______.__..... 4-5,6-38 structural relations of.___„.. — -...... ___..__.__.______. 71-72 Wakefield marble, deposition of-....-__-______— _--_ — —_————_-__. 77 transverse faults in._-____..._.__.....____. — ...-..-.... — .. 73-75 descriptionof.__---__------— ------38-39 Paleozoic time, events of____-- — . — ._____._ — _-._--__.-_-_____.______.__ 76-77 name of-_____--- — — _—___---_------—------_____-..._-... 39 Palmer Lime & Cement Co-—-. — — .------...__._...... __...... 23,78 Warner Co., quarries of_---_..._------_------__---._ ' 33 Peach Bottom slate, age of._-----.--..--.-.-..----.-...----...... 52 Water supply for the area-..--____._____...____. . — -_-_-_-____.- f'82 Peach Bottom syncline, rocks of—— .______—.____ t _...... 45 Wentz syncline, description of.___...______.__.._... —— - 43,44,50,71 Peerless Brick Co., plant of_...... __.._....___.______.______81 West York, sections in and near_____.._....__..___- — ...... 17,29,30 Pennsylvania Topographic and Geologic Survey, work by....-...----...... 2 Willis Creek Valley, section in._.__.______.______-—.____. 23 Peters Creek quartzite, age and character of __--.-- —_- ——-._____------45,51 Windsor, population of- — — -_._..._.-----.------.-- —...... — ' 1-1 Pigeon Hills, altitude of------— ..--..------...------.. — --...... -...... 4 Wissahickon formation, age of_---__-_ — — ———,--___ — --- — — ---_— ' 52 rocks of.__.______.__...... -..-„.—...-. — ...... _...... 5-6,7 character and distribution of...... — _—___-_ .1- 39-42,44-45,46, pis. 9-11 section in...... __._____—__.____-__._-_--._...- — _..---.-....--.. 9 magnetite in.. _-_.___-___...... _-__.__.___------_----- 82 Pigeon Hills anticlinorium, description of— ___- — _-- — — — _- — _ — _-____ 59-60,64,75 name of-__._-_-._____.-_...._.-.-.-----.....__ — _— — -_..._ 39 Plank Road fault, features of---.--- — — -.-- —.-..-.-.-.-...... 74,75 origin of------49-50 Port Deposit, Md., igneous rocks near, ageof....------.-..--....--...... 53 Wrightsville, sections near.-.-__..------..-...._.--.--.---_-__..-. 15,20 Pottery Hill anticline, features of______...... ___.___.______61 Wrightsvillesyncline, description of.----—---- —------_-_-_--_... 64 Pre-Cambrian rocks, character and distribution of- ______. ___ 4,5-6 Pre-Cambrian time, events of..- _____-_____...___..._._____ 75,77 Yoe, population of______...______-_———------1 Pre-Triassic rocks, structure of...______._._...___....__ 59-73 Yoe syncline, description of—_-______.______-_—__. —. T . 43,70-71 See also Cambrian rocks; Ordovician rocks. York, population of.-_____-___--_-______.____-___-_— 1 section in...-.-_--__.------..—- ———— — - — -——-- — ------29 Qnantico slate, age of.--..____------_...... _.-._...... _ 51,52 water supply for—-___...__------_....__.__... — — — ———— 82 Quarries in the area....------.-.-----..---.--.--.._----__---. 23-25,30,33,78-82 York Stone & Supply Co., quarries of...-._._..._-..._-.-----..._.. 79 Quaternary rocks, description of.____.______.___..__.____ 59 York Valley Lime & Stone Co., quarry of______...____ 79 Yorkhaven sill, features of..._-.-.._....._._..___——...___— 57,58 Red Lion, population of..__-.-----..---_---.--.----.--___...___...... 1 water supply for,-.------—— ------_...... ____...... _.. 82 Zieglersill, features of_....______..._.__..._____..-.-:.____ 67 Resser, C. E., fossils identified by...... _____.._....___._ — _„__..._ 30,32 Zinn, Eli, Co., quarries of...__...... __..„.—„.__.. 28-29,79 o