If yon no longer need this pnblicatioa write to the Geological Survey in Washington for official mailing label to use in returning it 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