U.S. DEPARTMENT OF THE INTERIOR OPEN-FILE REPORT U.S. GEOLOGICAL SURVEY OF 2010-1265 SEA LEVEL CORRELATION OF MAP UNITS DESCRIPTION OF MAP UNITS WHITE HALL Qa QUATERNARY Alluvium (Holocene and Pleistocene?)—Clay, silt, and lesser sand with angular to QUADRANGLE

1000 Qa 1000 2000

18 FEET W. VA. 70 48 subrounded clasts, derived from local bedrock. Pebble-size (4–64 mm) fragments of 20 27 23 67 Unconformity sandstone, siltstone, quartzite and weathered shale are scattered throughout the deposits. W.VA. SM VA. 83 Dm 35 62 35 Winchester 21 34 In area underlain by the Martinsburg Formation, consists of light-olive-gray, yellowish-

17 72 57 78 B 62 \ 72 61 t TERTIARY ? gray, and pale-yellowish-orange, well-bedded to crudely bedded, planar-bedded clayey 27 84 _O 73 25 silt, with weathered shale fragments as much as an inch long. Thickness as much as 40 ft 75 25 Unconformity 30 Qa DSls 61 ANTICLINORIUM 30 ZONE 31 Terrace deposits (Tertiary?)—Rounded to subrounded, highly weathered cobbles, sand, MAP LOCATION Dm b t PERMIAN ? silt, and clay exposed along State Route 681 near the confluence of Isaacs Creek and Back PROVINCE Z_ Swbm Strasburg 70 30 FAULT Skr Creek 73 70 FORD St SD Dh Om SYNCLINORIUM 33 22 60 68 Breccia (Permian?)—Brecciated massive dolomite or dolomitized limestone; may be 42 Df b 28 82 Df silicified in places and contain black stringers or staining (Fe-Mn oxide?). Exposures Ojo Dfu 25 36 83 Df 29 CREEK occur in fields east of Frog Hollow and along the axis of the Welltown syncline FAULT PROVINCE 18 Dfl Dfu MOUNTAIN 16 18 Db BAILEY 31 _O BRANCH Dmch Dmc Dmch Dm Df Hampshire Formation (Upper Devonian)—Sandstone, mudstone, siltstone, and minor 19 Dh Dh shale. Sandstone, reddish-gray to brownish-gray, medium- to thick-bedded, in part mica- _O 18 Dm Dfl Dfl SD 30 ceous and (or) arkosic, commonly crossbedded, unfossiliferous. Mudstone, maroon red, 71 18 BACK Mount Pleasant syncline 32 weathers into small lumps. Siltstone and shale, reddish-brown to gray, exhibits strong Om 70 77 76 Db RIDGE 70 80 MEADOW B 37 \ cleavage. Exposed thickness of unit as much as 850 ft. Upper part of formation not SM 16 30 MOUNTAIN 17 Db 25 33 exposed in quadrangle. Lower contact placed at base of red-beds and at top of highest Z_ Probable unconformity WEST VIRGINIAVIRGINIA 66 70 80 Qa 78 72 81 Dmc DEVONIAN Harrisonburg 65 82 81 89 gray, fossiliferous sandstone and shale of the underlying Foreknobs Formation 78 90 34 Dm VALLEY FAULT 85 60 85 Dmch 81 83 05 Dmc SM 24 35 30 MASSANUTTEN Dmc 28 Foreknobs Formation (Upper Devonian)—Interbedded sandstone, siltstone, and minor 32 Dmch 24 Dm 88 Dfu shale; locally fossiliferous. The main unit (Df) contains coherent packages of thick- Om 30 42 24 75 16 Dmch bedded to massive sandstone which occur as two ridge-forming units that are mappable BLUE Mountain 18 42 BAILEY FORD ANTICLINORIUM 22 CREEK 22 51 75 22 55 Df throughout the study area. The upper ridge-forming unit (Dfu) consists of 5 to 6 masses of NORTH

15 15 70 Dm Dm 15 SYNCLINORIUM 16 Back Creek fault Dm thick, resistant interbedded sandstone, siltstone, and shale that form a prominent ridge in

22 DSls 14 80 the upper part of the formation; locally two or more masses form distinct ridges. The Qa 15 54 14 Dmn Dfl Om 85 66 SM 15 24 Db Swbm lower ridge-forming unit (Dfl) consists of 3 to 4 packages of thick-bedded to massive 21 North 15 85 20 70

Dmch Skr 16 43 22 resistant interbedded sandstone, siltstone, and shale which form a prominent ridge at the Om Unconformity BACK 19 St base of the formation. The interval (Df) between the two ridge-forming units consists of 10 47 36 thin- to medium-bedded sandstone, siltstone, and shale and typically occupies the drain- _O 12 DSls 65 15 Little North Mountain age area between the two ridges; commonly not well exposed. The lower contact with the GREAT 75 Ojo 47 62 58 Brallier Formation is gradational through about 300 ft and is mapped where an abrupt Z_ 85 Swbm 21 SILURIAN increase in fossiliferous sandstone beds greater than 6 in. occurs. Thickness about 1,700 ft Little 46 ZONE 23 18 60 72 _O 20 Skr SYNCLINE 50 Brallier Formation (Upper Devonian)—Interbedded shale, siltstone, and sandstone, 20 70 67 45 Db 17 35 dark-gray to greenish-gray, weathers light brownish-gray, sparsely fossiliferous. Grain FAULT 82 17 77 St FAULT 75 size increases irregularly upward in section; sandstone beds, 2 to 6 in. thick, become more Silurian through Mississippian rocks of the Valley and ANTICLINORIUM 70 73 SM 70 52 77 Ridge Province 16 42 abundant near top of formation. Shale that is thickly laminated with scattered siltstone 69 Qa Unconformity 74 SURFACE beds up to 3 in. thick makes up the bulk of the formation. The lower contact with the FAULT _O 80 80 74 DS Devonian and Silurian rocks of Massanutten Mountain

19 Om MOUNTAIN 77 Om underlying Mahantango Formation is a disconformity above a massive sandstone unit 87 Ojo 32 50 50 (Dmc) at the top of the Mahantango. A mappable contact is placed at the top of this RIDGE Oc Upper and Middle Ordovician Martinsburg PLEASANT 26 52 70 Om 87 57 45 sandstone. Thickness approximately 1,100 ft Formation On 35 MOUNTAIN 68 63 Om 32 34 On SM Cambrian through Middle Ordovician rocks, mainly MOUNTAIN Dfl 37 _O GREAT NORTH Oc 40 Op Mahantango Formation (Middle Devonian)—Mudstone, shale, siltstone, and minor 85 35 65 Dmc carbonate Oc PIE 26 SYNCLINE 30 45 Oc sandstone. Mudstone, dark-gray to olive-gray, hackly weathering, locally very fossilifer- SM Qa 29 52 23 Neoproterozoic and Lower Cambrian rocks

Oc Z_ 22 Op ORDOVICIAN ous; bedding obscure, spheroidal weathering common. Sandstone (Dmc, equivalent to Df Df 52 On of the Blue Ridge Province 11 Dm Clearville Siltstone Member of Jolley, 1983), medium-gray, fine-grained, medium- to MOUNT NORTH

B' _O FAULT

75 On thick-bedded, generally massive, locally fossiliferous; occurs as two units near top of 64 70 Dmc Unconformity Figure 1. -- General geologic map of the Great Valley Province in WELLTOWN Dfu Dmch formation separated by mudstone; total thickness as much as 380 ft. Chaneysville NORTH APPLE 10 85 Or northern Virginia showing the location of the White Hall 7.5-minute

60 Op Siltstone Member (Dmch) is predominantly massive darkgray siltstone and black 70 67 35 43 Apple Pie Ridge Fault Op quadrangle, and inset map of the White Hall quadrangle showing shaded Dfu 20 mudstone occurring in the lower part of the formation, locally fossiliferous, up to 850 ft LITTLE 10 72 77 _e relief and selected structural elements. Lithotectonic units on inset map: Om Or thick, grades into calcareous shale at base. Total thickness of entire formation ranges from WELLTOWN 62 70 41 Or MS, Mississippian through Silurian rocks of Valley and Ridge Province;

22 Df B’ 15 90 35 1,600 to 1,800 ft. Lower contact gradational; placed at base of olive-gray beds above Df Oc 28 _O, Cambrian and Ordovician rocks of the Great Valley Province to the Thrust fault -- teeth on upthrown block 55 45 62 underlying Marcellus Shale 1000 2000 FEET SEA LEVEL \ 1000 70 83 Os east of Little North Mountain, bounded by the North Mountain fault 67 14 Strike-slip fault -- arrows indicate relative motion 40 35 zone. Major folds in the Devonian shales, siltstones, and minor 40 On 35 Marcellus Shale and Needmore Shale, undivided (Middle and Lower Devonian)— 39 44 45 O_c Dmn sandstones are also shown. Anticline -- arrow indicates direction of plunge 90 70 88 90 Op 80 50 Black shale, silty shale, calcareous shale, and minor limestone. Thickness as much as 800 40 63 25 Db 39 34 80 CAMBRIAN ft; however, units are not well exposed in the quadrangle due to faulting and colluvial Syncline -- arrow indicates direction of plunge 12 40 _e 38 cover. Descriptions below are based upon mapping conducted in adjacent quadrangles 60 40 33 Overturned anticline 47 74 56 20 22 Marcellus Shale (Middle Devonian)—Shale, black to dark-gray, highly fissile, with Overturned syncline Dfl DSls 38 46 EXPLANATION OF MAP SYMBOLS 45 63 75 localized beds or concretions of dark-gray, argillaceous limestone or calcareous shale. 84 Forms thin, platy chips and weathers dusky yellowish-gray in exposed outcrops. Base of Db 81 Bedrock contacts -- Dashed where approximately located; dotted where concealed A Or 90 70 Alluvial contacts -- Identity and existence certain, location inferred Marcellus is marked regionally by the Tioga Metabentonite; not seen in outcrops but may 90 Swbm 45 82 be present in covered intervals. Thickness up to 700 ft _e 80 83 13 Faults -- Dashed where approximately located, dotted where concealed 40 72 APPROX. STRATIGRAPHIC COLUMN 50 75 Needmore Shale (Middle and Lower Devonian)—Calcareous shale, dark-greenish-gray 45 30 49 THICKNESS 50 to olive-gray, and dark-gray fissile silty shale; locally fossiliferous. Thickness about 100 68 Thrust fault -- teeth on hanging wall FORMATION and MEMBER LITHOLOGY 25 30 Skr (in feet) EXPLANATION Period 75 Stage

ft. Grades upward into the Marcellus Shale through a series of thin limestone beds. Base Fossils 25 53 ZONE b placed at top of coarse sandstone of underlying Oriskany Sandstone. Qa 75 St Strike-slip fault -- arrows indicate relative sense of movement Ojo 65 Alluvium and colluvium 0–40 ft 54 20 Regional unconformity 40 51 5 U Oriskany Sandstone, Helderberg Group, and Tonoloway Limestone, undivided 48 40 b Normal fault -- U, upthrown side; D, downthrown side SYNCLINE DSls Hampshire Formation Dmc 36 49 D (Lower Devonian and Upper Silurian)—Sandstone, limestone, and shale. Thickness as up to 850 ft 33 B 50 52 Dm \ 25 b 50 42 much as 800 ft; however, units are not well exposed in the quadrangle due to faulting and 47 b \ In cross sections, relative sense of movement is shown by arrows, and by: Major fault zone 40 46 45 12107-CO 90 35 55 Dh Or colluvial cover. Descriptions below are based upon mapping conducted in adjacent quad- 85 32 15 45 60 away from observer 43 90 23 b rangles 28 toward observer upper ridge-forming unit ANTICLINORIUM t 30 PLEASANT 500 ft 57 47 Om b 44 Dfl 30 Oriskany Sandstone (Lower Devonian)—Sandstone, light-gray, yellowish-gray-, or 43 25 Strike and dip of beds t Dfu 73 61 28 O_c yellowish-brown-weathering, medium- to coarse-grained, medium- to thick-bedded, Dmc St 35 Dmch 52 85 40 Os 37 80 s Foreknobs Formation 12106-CO 25 locally crossbedded, calcareous; locally conglomeratic with quartz pebbles up to 0.5 in. LITHOLOGIC PATTERNS 15 Db Dmn 38 Inclined 1700 ft Dm MOUNT 25 70 long; friable when weathered; contains molds of brachiopod shells. Base placed at top of MOUNTAIN 28 37 FAULT \ 17 80 72 90 cherty limestone of Licking Creek Limestone of Helderberg Group 25 20 Qa 35 33 Vertical Alluvium and colluvium 58 80 28 Os 31 O_c 65 48 75 Helderberg Group, undivided (Lower Devonian and Upper Silurian)—Limestone, Upper 30 11 35 37 30 NORTH Dm Overturned 25 FAULT 42 72 62 lower ridge-forming unit 12 20 25 medium- to dark-gray, fine-grained, irregularly bedded, fossiliferous; contains black or 700 ft Dmc 33 30 Sandy or silty shale 82 60 72 80 37 light gray to white chert nodules, lenses, and beds as much as 1.5 ft thick near top; some 65 43 25 Inclined; multiple observations at single point 62 50 53 72 \ 52 77 30 10 limestone is medium gray, coarse grained, crinoidal. Individual units cannot be distin- 86 40 51 GREAT 65 40 75 guished in the quadrangle due to faulting and colluvial cover. Lower contact placed at base 80 Overturned; multiple observations at single point Interbedded sandstone and siltstone 40 Qa 67 52 75 70 \ 11 of crinoidal limestone overlying shaly, laminated limestone of the Tonoloway Limestone 75 77 42 St 75 83 35 30 36 12 based on mapping in other areas 83 32 85 87 Strike and dip of joints--Point of observation at intersection of multiple symbols 75 75 13 90 50 15 Brallier Formation Interbedded siltstone and shale 75 74 35 1100 ft 72 57 45 30 40 RIDGE 55 25 25 30 Tonoloway Limestone (Upper Silurian)—Limestone and shale. Limestone, medium- 75 Inclined; widely spaced (spacing >1m) 70 47 s 35 gray to medium dark-gray, crinkly laminated to thin-bedded. Shale, medium-gray to 60 12 13 72 62 24 30 dark-gray, calcareous. Locally contains ripple marks and mud cracks. Base placed at top s 17 Inclined; moderately spaced (spacing >0.3m and <1m) Bedded sandstone 10 FAULT of Tavenner Sandstone Member (Butts and Edmundson, 1966) of the Wills Creek Forma- _e 22 45 30 tion (not exposed in quadrangle) 15 Dmn 50 50 Inclined; closely spaced (spacing <0.3m) Clearville Sandstone Member 380 ft 11 30 45 70 Argillaceous or shaly sandstone 25 25 90 15 Wills Creek Formation, Bloomsburg Formation, and McKenzie Formation, undi- s Vertical; moderately spaced Swbm Qa 71 12108-CO 15 47 vided (Upper and Lower Silurian)—Shale, sandstone, siltstone, and limestone. Thick- 15 56 71 34 Mahantango Formation Strike and dip of cleavage ness as much 275 ft 1600–1800 ft Clay or clay shale

40 s 27 59 12102-CO È 62 90 89 25 30 \ 30 54 Wills Creek Formation (Upper Silurian)—Interbedded shale, siltstone, limestone, and A 36 Inclined 20 80 57 25 sandstone. Shale, medium-dark-gray and greenish-gray to light-olive-gray, weathers N A D E V O N I \ 69 Silt, siltstone, or shaly silt 83 81 25 15 10 53 30 yellowish-gray to reddish-gray, crinkly laminated, calcareous. Siltstone, greenish-gray to Chaneysville Siltstone Member 850 ft 57 56 25 Inclined; multiple observations at single point PIE 25 53 gray, weathers dark brownish-gray or grayish-yellow. Limestone, medium-dark-gray to 40 20 22 MOUNTAIN 85 40 MOUNTAIN 48 90 81 62 olive-gray, very fine grained with local interclastic flat-pebble conglomerate. Sandstone 20 85 Vertical; multiple observations at single point Carbonaceous shale 30 \ 67 65 primarily near top of unit, massive weathering, crossbedded, 15 to 20 ft thick, named Middle s 85 45 35 \ 67 42 80 52 46 20 17 26 61 Tavenner Sandstone Member by Butts and Edmundson (1966). Thickness of formation Dmch 34 50 Strike and dip of tension gash 40 42 78 72 35 80 45 140 to 180 ft 45 80 33 Calcareous shale 15 23 90 20 16 46 33 40 Df s 50 Vertical Dfl Dfu 50 s 63 83 30 Bloomsburg Formation (Upper Silurian)—Interbedded sandstone, siltstone, mudstone, Marcellus Shale 700 ft Db 47 30 30 Skr Inclined; multiple observations at single point and shale. Sandstone, reddish-brown to grayish-red, and gray, fine- to medium-grained, Crossbedded sandstone 40 Df Os 60 St 67 thin- to thick-bedded. Siltstone, grayish-red, reddish-brown, grayish-purple, medium- 41 35 90 Ojo 90 47 40 NORTH 60 gray, light-olive-gray, and greenish-gray, thin- to medium-bedded, shows prominent 52 ANTICLINE Vertical; multiple observations at single point 65 O_c 40 35 80 42 cleavage. Mudstone maroon-red, weathers dusky pale red, forms cohesive lumps in Needmore Shale 74 100 ft Conglomerate 52 37 60 outcrop. Shale, gray, greenish-gray, and reddish-brown. Lower contact is at base of red 40 \\ 40 90 \ Oriskany Sandstone 100 ft 55 60 Folds -- Showing trace of axial surface; large arrowhead indicates direction of plunge. sandstone beds

40 58 RIDGE 46

52 Dfu APPLE 40 40 FAULT Dashed where approximately located Cherty limestone 60 M McKenzie Formation (Upper and Lower Silurian)—Shale and siltstone. Shale, 60 SYNCLINE

47 (

O_c Lower 300 ft

Om 10 66 yellow-tan with silky luster, olive-gray and light-olive-gray, fissile, and fossiliferous. 48 49 Df 55 Syncline Helderberg Group

25 Qa 47 52 35 F Siltstone, yellow-gray, calcareous 50 43 35 O_c Fossiliferous clastic limestone 51 50 ( Dfl s 48 b PUMPKIN

50 60 Anticline

22 12104-CO 51 32 39 Keefer Sandstone and Rose Hill Formation, undivided (Lower Silurian)—Quartzite, 67 4 P 52 31 42 57 ( 70 12105-CO Skr

25 90 52 sandstone, and shale. Thickness approximately 500 ft Db 61 80 Overturned syncline Limestone

78 40 52 80 80 Tonoloway Limestone 400 ft 40 LITTLE 20 55 70 55 I

80 ( 90 42 40 b Keefer Sandstone—Quartzite, medium-light-gray, coarse-grained to pebbly, massive, 79 53 s Overturned anticline 7 30 51 50 s Or vitreous at base, grading up to medium-gray, medium-grained, and olive-gray, fine- Nodular or irregularly bedded limestone 83 63 22 WELLTOWN Spring -- Tail indicates direction of flow grained. Thickness about 130 ft NORTH _e 30 30 15 40 Upper 140–180 ft 50 90 20 Rose Hill Formation—Sandstone and shale. Sandstone, reddish-brown, grayish-red, Wills Creek Formation 49 WELLTOWN Sinkhole Argillaceous or shaly limestone

12 50 50 90 28 grayish-purple, and gray, medium- to coarse-grained, medium- to thick-bedded. Shale, Dm 20 85 49 55 88 12104-CO gray, greenish-gray, and reddish-brown, locally silty, and hackly weathering, locally Dm Dmn Os 23 33 Conodont fossil locality -- Showing collection number; sample information is linked to locality in the Dh Qa 16 11 Dmc Dmch Skr 50 16 75 fossiliferous. Lower contact placed at base of red sandstone overlying massive quartzite 44 St Ojo Or 43 25 25 digital geodatabase. Quartzite 84 40 90 75 Bloomsburg Formation 24 A' \ ledges of Tuscarora Quartzite. Thickness about 370 ft 48 40 20 Os A and 95–135 ft Photograph location -- Images are included in the digital geodatabase and linked to locality. A and B refer McKenzie Formation to sites shown in Figure 2 Tuscarora Quartzite (Lower Silurian)—Quartzite, light- to medium-gray, medium- to Crossbedded subgraywacke Base from U.S. Geological Survey, 1965 ° Geology mapped by R.A. Parker 1992–1993, St 01 SCALE 1:24 000 coarse-grained, thick-bedded, some beds conglomeratic. Base placed at bottom of quartz- Polyconic projection. 1927 North American datum and by D.H. Doctor, R.C. Orndorff, D.J. Weary, 10,000-foot grid ticks based on Virginia coordinate system, north zone CITENGAM HTRON 1 1/2 0 1 MILE ite ledges. Thickness about 250 ft Keefer Sandstone 130 ft HTRON EURT HTRON and J.E. Repetski 2006–2009 1,000-meter Universal Transverse Mercator grid ticks, zone 17, shown in blue 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET Interbedded limestone and shale Juniata Formation and Oswego Sandstone, undivided (Upper Ordovician)- N A U R I S I L To place on the predicted North American datum 1983 1 .5 0 1 KILOMETER Ojo Sandstone, shale, and conglomerate. Thickness about 250 ft Rose Hill Formation move the projection lines 7 meters south and 23 meters west 370 ft as shown by dashed corner ticks APPROXIMATE MEAN Dolomitic limestone DECLINATION, 2007 CONTOUR INTERVAL 20 FEET W.VA. Juniata Formation—Sandstone and shale. Arkosic sandstone, grayish-red to brown, fine- to coarse-grained, thin- to medium-bedded, locally thick-bedded, crossbedded. Lower VIRGINIA Shale or mudrock, grayish-red; occurs as thin beds and partings, mostly near top of forma- Cherty dolomite tion Bend in section GREAT NORTH MOUNTAIN MOUNT PLEASANT MAP LOCATION WELLTOWN PUMPKIN RIDGE Tuscarora Quartzite

North Mountain fault zone 250 ft FEET Little North Mountain fault Apple Pie Ridge fault Oswego Sandstone—Sandstone and conglomerate. Sandstone, greenish-gray, coarse- A Dh Df ANTICLINORIUM SYNCLINE SYNCLINE ANTICLINE A' FEET Dolomite

Welltown fault Welltown grained, thick-bedded, conglomeratic. Conglomerate, interbedded with sandstone, 3000 3000 composed of rounded clasts of chert and sandstone. Sandstone friable where locally Or calcareous and fossiliferous Dfu Silty limestone Juniata Formation 150 ft 2000 2000 Df Df Or Martinsburg Formation (Upper and Middle Ordovician)—Interbedded shale and Df Os Om Dfl lesser graywacke-siltstone and graywacke-sandstone. Shale, medium-gray to dark-gray Sandy limestone Dmc and light-olive-gray, weathers grayish-orange and dark yellowish orange, commonly silty, Oswego Sandstone 100 ft Dh SURFACE 1000 1000 generally noncalcareous, although calcareous intervals occur in lower part of formation (Stickley Run Member). Siltstone and sandstone (immature, generally lithic graywacke), Sandy dolomite Db Dmch Dm O_c medium-gray, grayish orange weathering, very fine to fine-grained, commonly graded

SEA LEVEL Upper SEA LEVEL (fining upward), lenticular, slightly calcareous to noncalcareous; contains many small Dfu O_c O_c Os Martinsburg Formation crossbeds. Graywacke is more abundant and more thickly bedded higher in section where Silty dolomite Db _e it forms conspicuous ribs in creek beds and may constitute as much as 30 percent of some 5000+ ft 1000 1000 Dfl intervals that are several hundred feet thick. Thicker beds are generally graded and DSls display characteristics of complete Bouma cycles. Regional thickness may be more than Argillaceous or shaly dolomite _e 5,000 feet Stickley Run Member 2000 2000 Swbm Chambersburg Formation (Middle Ordovician)—Interbedded limestone and calcare- Om Oc 500 ft ous shale. Limestone, medium-gray to medium-dark-gray, fine- to medium-grained, thin- Chambersburg Formation 3000 3000 to thick-bedded, irregularly bedded, knobby weathering. Calcareous shale, medium- Swbm St 1000 feet = 305 meters Skr Dmn Dm Dmn dark-gray to very dark-gray. Thickness as much as 500 ft New Market Limestone 160 ft Surficial deposits not shown Dm Skr Ojo Middle Dmc Dmch DSls New Market Limestone (Middle Ordovician)—Limestone, medium-gray and dove- On Pinesburg Station Dolomite up to 700 ft COMMONLY OCCURRING FOSSILS DISCUSSION gray, weathers very light-gray, thick-bedded, micritic, fenestral. Lower 10 ft is medium- Brachiopods KARST FEATURES AND HYDROLOGY gray to light-gray, thin-bedded dolomitic limestone interbedded with light-gray dololami- INTRODUCTION STRUCTURE nite. Base placed at top of uppermost medium-gray, thick-bedded dolostone of Pinesburg Gastropods Karst refers to a type of terrain that develops due to solution of bedrock Station Dolomite (Op) and below dolomitic limestone of the New Market. Exposed thick- Corals The White Hall quadrangle is located within the Valley and Ridge province Tectonic deformation of the bedrock in the White Hall quadrangle took along groundwater flowpaths, resulting in voids at depth. Features typical of karst ness approximately 160 ft of northern Virginia and the eastern panhandle of . The quadrangle place during the Alleghanian orogeny of the Late Paleozoic Era when the North terrain include sinkholes and shallow closed depressions (dolines), sinking streams, N A O R D V I C Bryozoans includes the physiographic regions of the northern Great Valley to the southeast, the American continent collided with the continents of Africa and Europe, forming the springs, and caves. Karst development is pervasive in the Cambrian and Ordovician A Pinesburg Station Dolomite (Middle Ordovician)—Dolostone and dololaminite, Op Crinoids narrow ridge of Little North Mountain along the western edge of the Great Valley, supercontinent Pangea. Erosion has predominated during the last 280 m.y., resulting carbonate rocks in the northern Shenandoah Valley (Hubbard, 1983; Orndorff and medium- to light-gray, weathers buff-yellow to very light-grey, fine-grained, thick-bedded 1,200 ft and the broad region of elongated valleys and ridges east of Little North Mountain. in the present landscape. Rockdale Run Formation Goggin, 1994). In the White Hall quadrangle karst development occurs in all of the to massive, with minor white and light-gray chert nodules. Weathered surfaces exhibit Burrows Early geologic mapping in the White Hall quadrangle was conducted by Butts and The quadrangle lies across the northeast plunge of the Great North carbonate rocks. Caves are not prevalent in the quadrangle; only one cave is known "butcher-block" (cross-hatched joints) structure. Also contains a few thin, medium-gray, Edmundson (1966), who mapped the Frederick County, Va., portion at a scale of Mountain anticlinorium (Butts and Edmundson, 1966) and includes several other and it occurs within the middle limestone of the Elbrook Formation. The cave is a fine-grained limestone beds in lower part. Paleokarst features of irregular bedding and Ostracodes 1:62,500. Lessing and others (1994) mapped the West Virginia portion of the regional folds. Folds tend to verge to the northwest, reflecting the tectonic transport former phreatic passage extending down the dip of bedding for approximately 200 collapse breccia common near top of unit; breccia may be silicified, with localized iron Graptolites

quadrangle at a scale of 1:24,000. Dean and others (1994) and Lessing and others direction, and trend to the northeast approximately 28º to 30º with gentle plunges to Beekmantown Group ft, with ephemeral standing water at the bottom. Springs occur mainly near or on mineralization. Lower contact placed at base of lowermost light-gray, thick-bedded dolos- Lower (1994) refer to the prominent curvilinear ridge extending into the northeast corner of either the north-northeast or south-southwest. The Mount Pleasant syncline, faults. It is noteworthy that several perennial springs in the quadrangle were found tone overlying dominantly limestone cycles of the Rockdale Run Formation. Exposed Nautiloids the quadrangle as North Mountain, whereas Butts and Edmundson (1966) refer to it centrally located within the quadrangle, is a doubly-plunging syncline that has thickness as much as 700 ft near the crest of Apple Pie Ridge, especially near zones of tight folding or to the east Trilobites as Little North Mountain. Despite the label of North Mountain on the topographic steeply dipping overturned beds on the east limb. This is the northernmost extent of of southeast-dipping thrust faults. Most of these are smaller springs (<1 cubic foot base map, this ridge is referred to as Little North Mountain in this report to avoid a regional syncline that spans all of Frederick County (Butts and Edmundson, per second), and several flow over the surface for a short distance before sinking Rockdale Run Formation (Middle and Lower Ordovician)—Interbedded limestone Stonehenge Limestone Conodonts Or 770 ft confusion with Great North Mountain immediately to the southwest and to preserve 1966). To the north, the southernmost extent of the Bailey Ford anticlinorium again. The largest springs in the quadrangle are located within the Stonehenge and dolostone. Limestone, bluish-gray, medium-gray, and dark-gray, fine- to medium- Stromatolites continuity with the nomenclature of this feature as it extends farther south in plunges out southwestward into a complex series of synclines and anticlines lying Limestone, southeast of the village of Green Spring. Sinkhole development is grained, thin- to medium-bedded, fossiliferous. Dolostone, medium-gray, fine- to Virginia. parallel to the Mount Pleasant syncline. To the west and southwest, many concentrated along faults, along the axis of the Welltown syncline, and within the medium-grained, medium-bedded, crystalline. Lithologies occur as fining upward Stoufferstown Member 80 ft STRATIGRAPHY northeast-plunging folds nose out and represent the northeastern extent of the Great nose and axis of the Pumpkin Ridge anticline; however, sinkholes occur within all carbonate cycles capped by dololaminite beds as much as 2 ft thick. Limestone beds also North Mountain anticlinorium and the southwestern extent of the Meadow Branch of the carbonate rock units, especially where the rocks have undergone locally contain intraformational conglomerates, algal bioherms, bioclastic zones, and burrow All exposed bedrock outcrops are sedimentary deposits of Paleozoic age synclinorium. To the southeast, the main folds are the Welltown syncline and the intensified deformation through folding, faulting, or some combination (see also mottling. Gastropod Lecanospira is common in lower and middle parts of formation. ranging from the Middle Cambrian Period to Late Devonian Period, approximately Pumpkin Ridge anticline; both plunge to the south. A notable anticline plunges to Hubbard, 1983). Along the North Mountain fault zone, sinkholes pond water as they Lower contact placed at base of lowermost crystalline dolostone or dololaminite bed Conococheague Limestone 2800 ft 515 to 365 Ma. These clastic and carbonate sedimentary strata reflect nearshore and the northeast at the eastern edge of the map area and contains the only exposure of collect surface runoff in the wet season, although they eventually drain (Fig. 2). overlying dark-gray, thick-bedded limestone of the Stonehenge Limestone. Exposed UNIT CONVERSION FACTORS offshore marine and deltaic depositional environments. The deposits indicate minor the Middle Ordovician rocks in the quadrangle. After being formed, this anticline Upper Areas of low elevation formed within the carbonate rocks permit rapid internal thickness approximately 1,200 ft; thickness uncertain due to faulting and folding 1 inch (in.) = 25.4 millimeter (mm) cyclic sea level transgression and regression along a passive continental margin subsequently was cut by faults having relatively limited displacement (several drainage, and constitute zones of focused groundwater recharge. 1 foot (ft) = 0.3048 meter (m) Big Spring Station Member during the Late Cambrian to Middle Ordovician Periods, to major sea level changes thousand feet). The anticline is itself thrust up over the eastern limb of the Stonehenge Limestone (Lower Ordovician)—Limestone, dark-gray, fine- to medium- 295 ft 1 mile (mi) = 1.609 kilometer (km) resulting from tectonic uplift during the Late Ordovician part of the Taconian corresponding syncline; this limb extends to the southwest where it ends at another REFERENCES CITED Os grained, thick-bedded to massive, fossiliferous, with crinkly laminations and minor black 1 cubic foot per second (cfs) = 0.02832 cubic meter per second (m3 /sec) orogeny. Depositional environments (from oldest to youngest) include (1) broad thrust fault near Green Spring. Outcrop-scale folds are parasitic on regional folds B chert. Also contains algal bioherms, intraformational conglomerates, bioclastic beds, and shallow marine shelf represented by the carbonate rocks of the Late Cambrian to and appear to represent local adjustments during the same phase of folding. Two Butts, Charles, and Edmundson, R.S., 1966, Geology and mineral resources of Frederick County: Virginia Division of Mineral Resources Bulletin 80, 142 p., 1 map as plate, scale 1:62,500. minor dolostone beds. Gastropod Lecanospira is common in middle part of formation. Middle Ordovician Periods; (2) continental slope and foreland basin, represented by zones of tight minor folds are evident in the Elbrook Formation, one zone located at Massive limestone may show mottles from dolomitic burrows. Contact with underlying

C A M B R I A N A M B R I A C 2500+ ft deposits of shale and turbiditic flysch in the Upper Ordovician; (3) nearshore the village of White Hall, and the second along Braddock Road. A late-stage Dean, S.L., Lessing, Peter, and Kulander, B.R., 1994, Geology of North Mountain in eastern West Conococheague Limestone is gradational; base placed at first dark-gray limestone with Elbrook Formation marine, represented by sandstones, limestones, and shales of the uppermost cross-strike fault (Orndorff, 1992) is seen along Hiatt Run on the west limb of the Virginia [abs]: Geological Society of America, Abstracts with Program, v. 26, no. 4, p. 10. crinkly siliceous laminations (Stoufferstown Member) and above the uppermost dolos- Middle Ordovician to lower Devonian; (4) marine basin and river delta, represented by Welltown syncline, with smaller faults radiating around the nose of the fold further tone that caps Conococheague carbonate cycles. Thickness approximately 770 ft siliciclastic shales, siltstones, and minor sandstones of the Early to Late Devonian north. Giles, A.W., 1942, Structure of Little North Mountain of the north-central Appalachians: Journal of Any use of trade, product, or firm names is for descriptive purposes only Geology, v. 50, no. 8, p. 961–980. and does not imply endorsement by the U.S. Government Periods (Orndorff and others, 1999). These strata account for about 21,700 ft of The North Mountain fault zone cuts through the eastern part of the Conococheague Limestone (Lower Ordovician and Upper Cambrian)—Interbedded O_c section. quadrangle; it is a series of thrust faults generally oriented northeast–southwest that Hubbard, D.A., Jr. 1983, Selected karst features of the northern Valley and Ridge province, Virginia: s limestone, dolostone, dololaminite and sandstone. Limestone, medium-gray, fine-grained, Topographic ridges in the quadrangle are held up by the resistant separate the Silurian and Devonian shales, siltstones and sandstones from the Virginia Division of Mineral Resources Publication 44, 1 map sheet, scale 1:250,000. thin- to medium-bedded. Dolostone and dololaminite, light-gray, fine-grained, medium- N sandstones and quartzites in the Tuscarora Quartzite (St) or Keefer Sandstone and Cambrian and Ordovician carbonate rocks and shales (Fig. 1). The North Mountain bedded. Sandstone, light-gray to buff, orange-reddish weathering, medium- to coarse- MAPPING RESPONSIBILITY Jolley, R.M., 1983, The Clearville Siltstone Member of the Middle Devonian Mahantango Formation Rose Hill Formation (Skr), as on Little North Mountain. Lower ridges west of Little fault zone widens north of Strasburg, Va. to north of Winchester, Va., and multiple grained, calcareous. Limestone lithologies include intraformational conglomerates, algal North Mountain are underlain by sandstones in the Foreknobs (Df) or Mahantango splays of the primary thrust fault are evident in the White Hall quadrangle. The two in parts of , , West Virginia, and Virginia: Chapel Hill, N.C., University of North Carolina, M.S. thesis, 192 p. bioherms, ribbon rock, and oolites. Lithologies occur as carbonate cycles. Lower 295 ft, (Dm) Formations. East of Little North Mountain, the prominent Apple Pie Ridge is faults bounding the fault zone are the Little North Mountain fault and the Apple Pie Big Spring Station Member, consists of gray to buff, orange-reddish weathering, coarse- A held up by limestone and shaly dolomite of the Elbrook Formation (Єe) that has Ridge fault. The Little North Mountain fault lies on the west side of Little North Lessing, P., Dean, S.L., and Kulander, B.R., 1994. Geology of the White Hall quadrangle, Berkeley grained calcareous sandstone; medium-gray, fine-grained limestone with intraformational been thrust up along the Apple Pie Ridge fault. Other ridges in the carbonate units Mountain and brings Silurian and Lower Devonian rocks onto Middle Devonian County, West Virginia: West Virginia Geological and Economic Survey Open File Report OF–9406, conglomerate; and light-gray, fine-grained dolostone. Sandstone beds (s) also occur in 10p., with 1 map sheet, scale 1:24,000. are held up by thin sandstone beds within the Conococheague Limestone (OЄc) or shales. The Apple Pie Ridge fault (Orndorff and others, 2003) thrusts the oldest middle part of formation and form ridges. Upper part of formation contains very light- B highly siliceous beds at the base of the Stonehenge Limestone (Os). rocks exposed in the quadrangle (Elbrook Formation) onto the Lower Ordovician Orndorff, R.C., 1988, Latest Cambrian and earliest Ordovician conodonts from the Conococheague and gray weathering, medium-gray limestone with thin siliceous laminae. Base placed below Placement of contacts between the Lower Ordovician carbonate rock units Stonehenge Limestone and Conococheague Limestone. Dean and others (1994) Stonehenge Limestones of northwestern Virginia: U.S. Geological Survey Bulletin 1837–A, 23 p. lowermost calcareous sandstone bed of Big Spring Station Member. Thickness is approxi- were aided by the collection and identification of conodont fossils (Orndorff, 1988). named the thrust splay along the west side of Little North Mountain beginning at mately 2,800 ft On the east limb of the Welltown syncline the contacts between the Rockdale Run Green Spring the Back Creek fault; this is probably the northern extension of the Orndorff, R.C., 1992, Tectonic significance of cross-strike faults in the central Appalachian Great Valley of Maryland and West Virginia: Southeastern Geology, v. 32, no. 4, p. 197–214. W E Formation (Or), Stonehenge Limestone, and Conococheague Limestone were Little North Mountain fault. The Back Creek fault has been traced approximately 24 Figure 2. Seasonal photographs of focused internal drainage of surface water. Both sites A and B are labeled on the map and are located near thrust faults in the Elbrook Formation (Middle Cambrian)—Interbedded limestone, dolostone, and shale. C _e placed using the conodont fossil assemblages found at the junction of State Route mi northward from Green Spring into Maryland and converges with the North Cambrian-Ordovician carbonate units east of the North Mountain fault zone. Closed depressions (sinkholes) collect surface runoff during snowmelt, which ponds Limestone, medium-gray, fine- to medium-grained, thin- to medium-bedded. Dolostone, Orndorff, R.C., Epstein, J.B., and McDowell, R.C., 1999, Geologic map of the Middletown quadrangle, and infiltrates over the course of days to a few weeks. These depressions are normally dry in summer, as seen in summer (right) photo of site A. 672 and Welltown Road, just south of Galilee Church. Conodont fossil assemblages Mountain fault zone at McCoy’s Ferry, Md.; thus, the ridge of Little North Frederick, Shenandoah, and Warren Counties, Virginia: U.S. Geological Survey Geologic Quadrangle light- to medium-gray, yellowish weathering, fine-grained, medium-bedded. Shale, gray, also aided in placing contacts between carbonate units within the carbonate duplex Mountain is a large horse (Dean and others 1994). Interruptions in the outcropping Map GQ–1803, scale 1:24,000. yellowish weathering, dolomitic. Limestone contains algal bioherms, intraformational along the North Mountain fault zone. of the Tuscarora Quartzite along the Little North Mountain fault likely resulted from conglomerates, and dolomitic burrow mottles. Lowest beds exposed are bluish-gray, Orndorff, R.C., and Goggin, K.E., 1994, Sinkholes and karst-related features of the Shenandoah Valley Surficial materials include unconsolidated alluvium, colluvium, and cross-strike faulting rather than from thinning of sedimentary strata (Giles, 1942); medium- to thick-bedded limestone with dolomite ribbons and mottles and medium-gray, D terrace deposits of Quaternary age, and local paleo-terrace deposits possibly of however, lack of outcrop precludes precise mapping of faults in these areas. A in the Winchester 30' x 60' quadrangle, Virginia and West Virginia: U.S. Geological Survey Miscella- neous Field Studies Map MF–2262, scale 1:100,000. thick-bedded dolostone of the middle part of formation. Cycles of bluish-gray algal Tertiary age. Alluvium (Qa) was tentatively mapped along the larger streams; prominent north-south trending fault in the southeast part of the quadrangle area cuts limestone and grainstone and light-gray argillaceous dolostone occur in upper part of locally, low terraces may exist but have not been broken out within this unit. along the east limb of the Welltown syncline, and is herein named the Welltown Orndorff, R.C., Weary, D.J., and Parker, R.A., 2003, Geologic map of the Winchester quadrangle, Elbrook. A distinctive lithology is yellowish weathering, thin-bedded dololaminite that Colluvium (not mapped) covers most of the steeper slopes and fills the bottoms of fault. It is manifested by pronounced thinning of the Stonehenge Limestone and by Frederick County, Virginia: U.S. Geological Survey Open-File Report 2003–461, scale 1:24,000. appears shaly in weathered outcrops. Thickness is at least 2,500 ft; the thickness is many of the mountain hollows; it is composed mainly of quartzite and sandstone numerous calcite-filled tension gashes in limestone and shear structures within increased by intraformational folding boulders and cobbles, or fragments of chert. brecciated dolomite, observable in outcrops along the lineament. S

A,B - Lessing, Dean, and Kulander (1994); Parker, Doctor N = 56; Size of largest petal = 8.9% GEOLOGIC MAP OF THE WHITE HALL QUADRANGLE, FREDERICK COUNTY, VIRGINIA, AND BERKELEY COUNTY, WEST VIRGINIA B - Orndorff, Doctor Figure 3.—Equal area Rose diagram of joint orientations in the By C - Parker, Doctor White Hall quadrangle. Petals represents joint azimuths binned in Daniel H. Doctor, Randall C. Orndorff, Ronald A. Parker, David J. Weary, and John E. Repetski D - Doctor, Orndorff, Weary, Repetski 10º increments, dip to right of azimuth. 2010