Geologic units in Wythe county, Virginia

Additional scientific data in this geographic area

Rome Formation (Cambrian) at surface, covers 23 % of this area

Pumpkin Valley Shale and Rome Formation. Pumpkin Valley Shale (Bridge, 1945). Shale, light-greenish-gray to dark-greenish-gray, grayish-brown, and maroon; a few beds of similar colored siltstone; sparse beds of limestone and dolostone. The Pumpkin Valley Shale conformably overlies the Rome Formation. The formation is approximately 350 feet thick. Harris (1964) identified the Pumpkin Valley Shale of Southwest Virginia as a formation within the Conasauga Group; however, because of similar lithologies it is often indistinguishable from the Rome Formation and the two formations commonly are mapped together. Rome Formation (Hayes, 1891). Siltstone, shale, sandstone, dolostone, and limestone. Siltstone and shale, greenish-gray and grayish-red, laminated to thin-bedded. Sandstone, micaceous, locally glauconitic, greenish-gray and reddish-gray, very-fine- to medium-grained, thin-bedded. Dolostone, light- to dark-gray, aphanic to medium-grained, thin-to massive-bedded, with ripple marks and mudcracks. Lime stone, argillaceous, very-light-gray to dark-gray, thin- to medium- bedded. Carbonate rocks range from sparse 1- to 2- feet-thick beds in western Scott County to discontinuous units as much as 50 feet thick which comprise 30 to 40 percent of the formation in western Russell and Washington counties (Evans and Troensegaard, 1991; Bartlett and Webb, 1971). Maximum recorded thickness is 1500 feet in the Clinchport area (Brent, 1963); although this may have included the Pumpkin Valley Shale. A complete thickness has not been determined because the lowermost part of the Rome Formation is normally absent due to faulting.

Shady Dolomite (Cambrian) at surface, covers 19 % of this area

Shady Dolomite (Keith, 1903). Dolostone with minor limestone and shale divided into three members: Ivanhoe (upper) Member; Austinville (middle) Member, and Patterson (lower) Member. Ivanhoe Member, dark-gray, fine-grained limestone and minor interbedded black shale; 100 to 500 feeet thick. Austinville Member, very-light-gray to cream colored, fine- to medium-grained, crystalline or saccharoidal, massive-bedded dolostone with several sequences of interbedded limestone, very-dark-gray dolostone or mottled dolostone and shale; 1000 feet thick. Patterson Member, medium- to dark-gray, fine-grained, thin-bedded dolostone or limestone with siliceous partings and intraformational brec ia beds; 800 feet thick. The Shady Dolomite is gradational with the underlying Erwin Formation and the upper two members grade southeastward into shaly dolostone with biohermal mounds, intraformational limestone or dolostone breccias, oolitic limestone, and arenaceous limestone and dolostone. This upper,southeastern facies, is in part equivalent to beds in the lower Rome Formation (Pfi el and Read, 1980). The Shady is very poorly exposed except near New River in Wythe and Smyth counties where it is at least 2100 feet thick and where major lead and zinc deposits were mined from the upper members (Currier, 1935).

Erwin and Hampton Formations (Cambrian) at surface, covers 12 % of this area

Erwin Formation (Keith, 1903,1907). Quartzite, sandstone, and shale. Quartzite, light-gray to white, medium- to fine-grained, thick-bedded, cross-laminated, quartz cemented, and very resistant. Sandstone, ferruginous, dark-gray to bluish- black, medium- to coarse-grained, locally conglomeratic, and with various amounts of hematite cement, in medium- to thick-beds. Shale, silty and sandy, drab-greenish-gray, thin- to medium-bedded, non-resistant, comprises much of the formation but is poorly exposed. The Erwin is less than 1000 feet thick and is equivalent to the Antietam Formation and possibly the upper part of the Harpers Formation in northern Virginia. Hampton Formation (Keith, 1903). Shale, sandstone, and quartzite. Shale, dark-gray or dark-greenish-gray, fissile, very argillaceous, silty laminae common, with interbeds of siltstone and fine-grained, lithic sandstone. Sandstone, feldspathic, greenish-gray, vitreous, medium- to coarse-grained, pebbly, cross-laminated. Quartzite, white to light-brown, vitreous, fine-grained, medium- to thin-bedded, resistant, restricted to the upper part of the formation. The Hampton is largely equivalent to the Harpers Formation to the northeast and ranges in thickness from more than 1500 feet to about 1200 feet with the thinner sequence in the northwesternmost exposures.

Elbrook Formation (Cambrian) at surface, covers 12 % of this area

Elbrook Formation (Stose, 1906). Dolostone and limestone with lesser shale and siltstone. Dolostone, medium-to dark-gray, fine- to medium-grained, laminated to thick-bedded. Limestone, dark-gray, fine-grained, thin- to medium-bedded, with algal structures and sharpstone conglomerate. Shale and siltstone, light- to dark-gray, dolomitic, platy weathering, with minor grayish-red or olive-green shales. Interbedded limestone and dolostone dominate the upper part of the formation; dolomitic siltstone and shale and thin- bedded argillaceous limestone dominate the lower part. The formation ranges be tween 1500 and 2900 feet in thickness in the southeasternmost exposures but is incomplete elsewhere due to faulting. The Elbrook of northern Virginia is transitional with the Nolichucky and Honaker Formations (locally the limestone facies of the Nolichucky has been differentiated from the Elbrook by Bartlett and Biggs (1980). It is also approximately equivalent to the rock sequence comprised of the Nolichucky and Maryville Formations, the Rogersville Shale, and the Rutledge Formation. Farther southwest the Conasauga Shale is the Elbrook equivalent. The Elbrook appears to be conformable and gradational with the underlying Waynesboro or Rome Formations. From Washington County to Augusta County much of the Elbrook Formation adjacent to the Pulaski and Staunton faults is a breccia of the "Max Meadows tecontic breccia type" (Cooper and Haff, 1940). These breccias are composed of crushed rock clasts that range from sand size to blocks many feet long, derived almost entirely from the lower part of the Elbrook Formation. The breccia commonly forms low lands characterized by karst features.

Brallier Formation (Devonian) at surface, covers 6 % of this area

Brallier Formation (Butts, 1918). Shale, sandstone, and siltstone. Shale, partly silty, micaceous, greenish-gray, gray ish-brown and medium- to dark-gray, black, weathers light-olive-gray with light-yellow, brown and purple tints; black shale in thin beds and laminae, sparsely fossiliferous. Sandstone, micaceous, medium-light-gray, very-fine- to fine-grained, thin- to thick-bedded, and light-brown siltstone interbedded with shale. Locally siltstone is in very-thin, nodular, ferruginous lenses (Bartlett, 1974). Lower contact transitional; base at lowest siltstone bed above relatively nonsilty dark-gray shale. Equivalent to part of the Chattanooga Shale. Formation thins southwestward; it ranges from 940 feet in thickness in southwestern Washington County (Bartlett and Webb, 1971) to more than 2200 feet in Augusta County (Rader, 1967).

Conococheague Formation (Cambrian) at surface, covers 5 % of this area

Conococheague Formation (Stose, 1908). Dominantly limestone with significant dolostone and sandstone beds in lower part and locally in upper part. Limestone, medium- to very-dark-gray, fine-grained, thin-bedded with wavy siliceous partings that weather out in relief. Vertically repetitious primary sedimentary features such as sharpstone conglomrate, laminated bedding, and algal structures indicate cyclic sedimentation. Dolostone, medium-gray, fine- to medium-grained, laminated to massive-bedded with primary features similar to those in the limestones. Sandstone, medium-gray, brown weathering, cross-laminated, medium to thin-bedded, forms linear ridges, largely associated with dolostone beds but quartz sand common in most lithologies. Formation is present throughout the Valley of Virginia southeast of the Pulaski and North Mountain faults. It ranges in thickness from about 2200 feet in northern Virginia to 1,700 feet near Abingdon. The Conococheague is approximately equivalent to the Copper Ridge and Chepultepec Formations and conformably over lies the Elbrook Formation.

Maccrady Shale and Price Formation (Mississippian) at surface, covers 4 % of this area

Maccrady Shale and Price Formation. Refer to individual units for descriptions.

Chemung Formation (redefined as Foreknobs Formation) (Devonian) at surface, covers 3 % of this area

Chemung Formation (Hall, 1839). Redefined as the Foreknobs Formation (Dennison, 1970). Sandstone and shale, dark-gray and greenish-gray, fine-grained, thin- to thick-bedded, lithic sandstone and interbedded greenish gray, fissile, clay shale. Minor quartz-pebble conglomerate, thin red sandstone, and locally, fossil shell beds. Very thin or absent in southwestern Virginia; thickens to about 2500 feet northeastward in Frederick County. Gradational contact with underlying Brallier Formation and equivalent to part of the Chattanooga Shale to the southwest. Redefined and described as part of the Greenland Gap Group by Dennison (1970).

Price Formation (Mississippian) at surface, covers 2 % of this area

Price Formation (Campbell, 1894). Sandstone, quartzarenite, conglomerate, siltstone, shale, limestone, and coal. Sandstone, feldspathic, slightly micaceous, light-gray to medium-gray, weathers olive-gray to greenish-gray, few grayish-red beds, very-fine- to medium-grained, thin- to thick-bedded, cross-laminated in upper part of formation, locally conglomeratic with quartz pebbles and granules. The lowest part of the Price contains quartz pebble conglomerate and quartzarenite, with marine fossils in basal beds. Formation becomes finer grained to the southwest. Sandstone is dominant in the upper half of formation. Siltstone and silty shale, partly calcareous, locally pyritic and glauconitic, greenish-gray, medium-dark-gray to light-olive-gray, locally black and carbonaceous, laminated to medium-bedded, hard, hackly, fissile to platy, fossiliferous; interbedded with sandstone. Limestone, rare, argillaceous, arenaceous, very- thin beds, as much as six inches thick, in interbedded siltstones and shales (Bartlett, 1974, p. 83-84). Coal in upper part of formation (Bartholomew and Brown, 1992; Bartlett, 1974; Cooper, 1944). The Price is a westward thinning clastic wedge (Bartlett, 1974, p. 170) that is equivalent to part of the Grainger Formation in the southwesternmost part of Virginia. It overlies the Chemung Formation from southwestern Washington County to the north east and the Brallier Formation or the Chattanooga Shale to the southwest. Base is conformable, placed at the base of a conglomerate northeast of Lee County (Bartlett, 1974). Thickness is variable; it is 250 feet thick in Lee County, 185 feet thick (Henika, 1988) in Scott County and as much as 1800 feet thick (Campbell and others, 1925) in Montgomery County.

Millboro Shale, Huntersville Chert, and Rocky Gap Sandstone (Devonian) at surface, covers 2 % of this area

Millboro Shale, Huntersville Chert, and Rocky Gap Sandstone. Millboro Shale. Refer to previous description under Dmn. Huntersville Chert (Price, 1929). Chert, white, thin-bedded, iron-stained, blocky, fossiliferous with cherty, glauconitic sandstone and greenish-gray shale. The Huntersville Chert ranges from 10 to 60 feet in thickness (Bartlett and Webb, 1971). Butts (1940, p. 303) states, "The Onondaga [Huntersville Chert] persists to Mendota, Washington County, but 10 miles farther southwest it is absent in a fully exposed section". The Huntersville correlates with the Needmore Formation to the northeast and the upper part of the Wildcat Valley Sandstone in Lee County. Rocky Gap Sandstone (Swartz, 1929): Sandstone, medium- to light-gray, weathers dark-yellowish-orange, coarse-grained, scattered, thin, quartz-pebble conglomerate beds, arenaceous chert in upper ten feet, calcite cement, friable when weathered. Thickness ranges from 0 near McCall Gap, Washington County to about 85 feet in Bland and Giles counties. Equivalent in part to the Wildcat Valley Sandstone of Lee County and the Ridgeley (Oriskany) Sandstone and Helderberg Group north of Craig County. The lower contact is disconformable. The upper contact with the Huntersville Chert appears to be conformable.

Knox Group (Cambrian-Ordovician) at surface, covers 2 % of this area

Knox Group (Safford, 1869). Dolostone, limestone, and sandstone. Dolostone, light- to medium-gray, very-fine- to fine-grained, locally with pink streaks in the upper part; and very-light-gray to dark-gray and brownish-gray, medium- to coarse-grained, locally argillaceous dolostone near the base of the unit; greenish-gray shale partings locally present; chert is abundant in some parts of the unit. Limestone, blue gray to dark-blue-gray, very-fine- to coarse-grained, locally sandy. Sandstone, gray to brown, fine- to medium-grained. Limestone is dominant in the eastern thrust belts. The Knox Group ranges from 2000 feet in Southwest Virginia to 3560 feet in thickness to the east in Washington County (Bartlett and Webb, 1971). The Knox includes the Mascot, Kingsport, Chepultepec, and Copper Ridge Dolomites and the Maynardville Formation.

Moccasin or Bays Formation through Blackford Formation (Ordovician) at surface, covers 2 % of this area

Moccasin Formation, Bays Formation, Unit C, Unit B, and Unit A. Moccasin Formation (Campbell, 1894). Mudstone, shale, imestone, and sandstone. Mudstone and shale, dusky-red to dark-reddish-brown, calcareous, ripple-marks, and mud cracks common. Limestone, light-olive-gray, weathers very-light gray, aphanic with "birds-eyes", locally fossiliferous. The limestone generally is the middle member of the Moccasin southwest of Giles County. In eastern Giles County and northeastward a thin medium-grained, gray sandstone occurs near the base of the Moccasin. The thickness ranges from 0 in northern Alleghany County to about 600 feet in Scott County. Bays Formation (Keith, 1895). Siltstone, sandstone, mudstone, and limestone. Siltstone, grayish-red, olive- to light-olive-gray, locally calcareous, sandy in part. Sandstone, light-gray to yellowish-gray, fine- to very-coarse-grained, locally conglomeratic, calcareous. Mudstone, grayish-red, olive- to light-olive-gray, mudcracks common. Limestone, grayish-red to light-olive-gray, aphanic. Five distinct K-bentonites reported by Hergenroder (1966). Contacts are conformable except perhaps in Botetourt, Roanoke, and Montgomery counties. Thickness ranges from 105 feet north of Wytheville to 890 feet near Daleville in Botetourt County. From Scott and Washington counties to Highland County and northwest of the Pulaski and North Mountain faults, a multitude of stratigraphic names have been applied to the rocks between the Bays or Moccasin (above) and the Beekmantown or Knox (below). The lack of detailed geologic mapping, except in Scott and Giles counties, the restricted area of the two major stratigraphic studies (Cooper and Prouty, 1943; Kay, 1956), and the general disagreement as to mappability and correlation of units makes it impossible to apply specific stratigraphic nomenclature at this time. Therefore, the rocks are described as three packages of lithologies (from youngest to oldest): Unit C, Unit B, and Unit A. Unit C. Limestone, medium- to dark-gray, aphanic to fine-grained with thin, medium- to coarse-grained beds, argillaceous, nodular to planar-bedded, locally very fossiliferous. The following names have been applied to Unit C: Witten, Bowen, Wardell, Gratton, Benbolt, Chatham Hill, Wassum, Rich Valley, Athens, Ottesee, Liberty Hall, Fetzer, and Giesler. Unit B. Limestone, light- to dark-gray, aphanic to coarsegrained, black and gray chert nodules, carbonate mound buildups. This unit is characterized by grainstone with interbedded micrite and chert. The overlying Unit C is very argillaceous and lacks chert. The following names have been applied to Unit B: Wardell, Gratton, Benbolt, Lincolnshire, Big Valley, McGlone, McGraw, Five Oaks, Peery, Ward Cove, Rockdell, Rye Cove, Effna, Whitesburg, Holston, Pearisburg, and Tumbez. Unit A. Dolostone, light- to medium-gray, fine-grained, locally conglomeratic, cherty. Limestone, medium- to dark gray, fine-grained, locally cherty. Shale, light-gray to dusky red. A basal chert-dolomite conglomerate with clasts as much as cobble size is locally present on the unconformity surface. The following names have been applied to Unit A: Blackford, Elway, Tumbez, Lurich (lower part), and "basal clastics".

Juniata, Reedsville, Trenton, and Eggleston Formations (Ordovician) at surface, covers 2 % of this area

Juniata Formation (Darton and Taff, 1896). Siltstone, shale, sandstone, and limestone. Siltstone, shale, and sandstone, locally calcareous, grayish-red, locally fossiliferous; with some interbeds of greenish-gray shale, quartzarenite, and argillaceous limestone. Cycles consisting of a basal, crossbedded quartzarenite with a channeled lower contact; a middle unit of interbedded mudstone and burrowed sandstone; and an upper bioturbated mudstone are commonly present north of New River (Diecchio, 1985). The Juniata Formation ranges from less than 200 to more than 800 feet in thickness. In southwestern Virginia the red, unfossiliferous, and argillaceous Juniata Formation is present in the southeastern belts. It is equivalent to the gray, fossiliferous, and limy Sequatchie Formation of western belts (Thompson, 1970; Dennison and Boucot, 1974). Even though the beds along Clinch Mountain, in Scott County, contain minor amounts of carbonate rock (Harris and Miller, 1958) the majority is grayish- red siltstone, which is typical of the Juniata Formation. Reedsville Shale. Refer to description under Ou. Trenton Limestone. Refer to description under Ou. Eggleston Formation. Refer to description under Ou.

Silurian Formations Undivided (Silurian) at surface, covers 2 % of this area

Some landslides with intact stratigraphic units in Giles County area. Includes: Dsu, Skrt, Sm. (Shrc?)

Lower Devonian and Silurian Formations Undivided (Silurian-Devonian) at surface, covers 2 % of this area

Some landslides with intact stratigraphic units in Craig County area. Includes: Dsu, Skrt, Sm. (Shrc?)

Beekmantown Group (Ordovician) at surface, covers 1 % of this area

Includes the Pinesburg Station Dolomite, the Rockdale Run Formation, and the Stonehenge Limestone (northern Virginia only) or the Beekmantown Formation and Stonehenge Limestone (central and southwestern Virginia). Pinesburg Station Dolomite (Sando, 1956). Dolostone, dark- to light-gray, fine- to medium-grained, medium- to thick bedded with minor nodular white chert. It ranges from 0 to 400 feet in thickness and is equivalent to beds in the upper Beekmantown Formation. Present only in Clarke and Frederick counties and is conformable with the underlying Rockdale Run Formation and unconformable with the overlying New Market or Lincolnshire Limestones. Rockdale Run Formation (Sando, 1958). Dominantly limestone and dolomitic limestone, lesser dolostone with minor chert throughout. Limestone, light- to medium-gray, fine-grained generally, but coarse, bioclastic limestone locally, medium- to thick-bedded. Dolostone, light-gray, fine- to medium- grained, thick-bedded with "butcher block" weathering and minor nodular or bedded chert in both limestone and dolostone. Unconformably overlain by the New Market Limestone where the Pinesburg Station Dolomite is absent. It is laterally equivalent to the Beekmantown Formation and conformably overlies the Stonehenge Limestone. The formation is about 2700 feet thick. Beekmantown Formation (Clarke and Schuchert, 1899). Dominantly dolostone and chert-bearing dolostone with lesser limestone. Dolostone, light- to very-dark-gray, fine- to coarse grained, mottled light- and dark-gray, with crystalline beds locally contains nodular, dark-brown or black chert and thick, hill forming, lenticular chert beds in lower part. Limestone, very-light- to medium-gray, fine-grained, medium- to thick bedded, locally dolomitic and locally fossiliferous. The formation is present from Page and Shenandoah counties southwestward in the easternmost exposures of the Lower Ordovician rocks. It and the underlying Stonehenge Limestone, are equivalent to the Mas cot and Kingsport Dolomites of the upper part of the Knox Group. It is unconformably overlain by Middle Ordovician limestones and conformably overlies the Stonehenge Limestone. Erosion, related to the unconformity at the top of the Beekmantown Group and Knox Group, has produced erosional breccias, local topographic relief, and paleokarst topography as well as significant regional thinning of the rock units. The Beekmantown Group thins from about 3000 feet in Page County to less than 700 feet in Washington County, largely because of post-Beekmantown erosion. Stonehenge Limestone (Sando, 1956). Limestone with interbedded dolostone in north western Virginia. Limestone, dark-gray, fine-grained, laminated to massive, with black nodular chert. Dolostone, light-gray, fine-to very-coarse-grained, as thin- to medium-interbeds or as coarse- grained, massive, reefoidal bodies. Reefoidal bodies are restricted to the middle portion of the formation. The formation conformably overlies the Conococheague Formation and thins northwestward from 400 or 500 feet in the southeasternmost exposures (Page County) to a few tens of feet in the north western exposures (western Rockingham County) and is not recognizable or included in the lower Beekmantown or upper Conococheague in much of southwestern or western Virginia. It is equivalent to the lower part of the Kingsport Dolomite.

Knobs Formation, Paperville Shale, Lenoir and Mosheim Limestone (Ordovician) at surface, covers 0.8 % of this area

Knobs formation (Cooper, 1961). Shale, siltstone, sandstone, and conglomerate. Shale and siltstone, brown. Sandstone, lithic, greenish-brown, fine- to coarse-grained. Conglomerate, polymictic (rounded to subrounded clasts of limestone, dolomite, sandstone, quartzite, vein quartz, shale, chert, and feldspar in calcareous matrix). Some interbeds of calcareous siltstone and sandstone. The Knobs formation ranges from 800 to 3400+ feet in thick ness (the upper part of the unit is eroded) (Bartlett and Biggs, 1980). The Knobs formation corresponds to the upper member of the Athens Shale of Butts (1933) as described by Bartlett and Biggs (1980). Fincastle Conglomerate Member of the Martinsburg Formation. Conglomerate, sandstone, shale, and siltstone (Rader and Gathright, 1986). Conglomerate (type 1), poorly sorted, clast-supported, pebble to boulder clasts of limestone, dolomite, quartzite, sandstone, chert, vein quartz, granite gneiss, quartz pebble conglomerate, greenstone, and shale, subangular to subrounded. Conglomerate (type 2), poorly-sorted, matrix supported clasts of quartzite, vein quartz, limestone, and chert, subrounded to well-rounded. Matrix framework grains in both types are sand-size quartz, limestone, and dolomite with minor chlorite and sericite. The cement is calcite. The conglomerate fines upward from a scoured base to sandstone. Sandstone, lithic, medium- to very-coarse-grained, brownish-gray, cross stratification rare. Shale and siltstone, gray, convolute bedding common. This member is restricted to the Fincastle area of Botetourt County. Paperville Shale (Cooper, 1956). Shale, olive-gray to dark-gray, fissile, thin-bedded; with minor gray, argillaceous siltstone, fossiliferous in lower part. The Paperville Shale ranges from 200 to 2300 feet in thickness (Bartlett and Biggs, 1980). The Paperville Shale corresponds to the lower member of the Athens Shale of Butts (1933) as described by Bartlett and Biggs (1980). Lenoir Limestone (Safford and Killibrew, 1876). Limestone, argillaceous, gray to dark-gray, fine-grained, medium bedded, silty laminations, fossiliferous. Lower contact is unconformable. The Lenoir Lime stone ranges from 0 to 70 feet in thickness (Bartlett and Biggs, 1980). Mosheim Limestone (Ulrich, 1911). Limestone, aphanic, medium-bedded with calcite crystal clusters, sparsely fossiliferous; limestone-dolomite-chert clasts in aphanic limestone matrix common at base of unit; rare thin interbedded dolomite. Unconformable with underlying unit. The Mosheim Limestone ranges from 0 to 150 feet in thickness (Bartlett and Biggs, 1980). The Lenoir and Mosheim Limestones have a combined thickness up to 270 feet in southwestern Washington County (Bartlett and Webb, 1971). In the Fincastle Valley the nomenclature Lincolnshire and New Market Limestones replaces Lenoir and Mosheim Limestones of older reports.

Nolichucky and Honaker Formations (Cambrian) at surface, covers 0.7 % of this area

Nolichucky Formation. Refer to description under [nmrr]. Honaker Formation (Campbell, 1897). Dolostone, limestone, and shale. Dolostone, light- to dark-gray to dark-bluish-gray, aphanic to coarse-grained, thin- to massive-bedded, "butcher-block" weathering; with sparse interbeds of argillaceous limestone, and minor dark-gray chert. Limestone, argillaceous, ribbon-banded in part, light- to medium-gray, very-fine-grained, thick-bedded. Shale, greenish-gray, laminated to thin-bedded. The Honaker Formation is predominantly dolostone with subordinate limestone. The dolostone becomes more dominant in the northeastern part of outcrop belt (Evans and Troensegaard, 1991). Shale is locally present as a 20- to 60-feet-thick unit in the middle of the formation and as thin interbeds with the dolostone and limestone throughout the area. The Honaker Formation ranges from about 1000 to 1100 feet in thickness. It is laterally equivalent to the lower Elbrook to the east.

Unicoi Formation (Cambrian) at surface, covers 0.3 % of this area

Unicoi Formation (Keith, 1903,1907). Sandstone and quartzite with phyllite, tuffaceous phyllite, conglomerate, and minor basalt. Sandstone, lithic or feldspathic, pinkish-gray to dark-greenish-gray, fine- to coarse-grained, angular, poorly sorted, locally conglomeratic. Quartzite, largely in upper part of the unit, white, pale-green, or gray, vitreous, medium- to coarse-grained, locally feldspathic, medium- to very-thick bedded, very resistant to weathering and erosion. Phyllite, reddish-, purplish-, or greenish-gray, as thin, sparse interbeds throughout, with purple tuffaceous phyllites in lower part. Conglomerate, fine- to coarse-polymictic-pebble conglomerate, medium- to thick-bedded, with lithic clasts and quartz pebbles. Basalt, very-dark-grayish-green, aphanitic, locally amygdaloidal; in one to three beds a few feet thick in the lower part only. Upper part has more quartzite and contains phyllite beds similar to the overlying Hampton Formation. Lower part is very feldspathic, contains most of the conglomerate beds and all of the volcanic rocks. The Unicoi is present from Augusta County to Tennessee and is laterally equivalent, at least in part, to the Weverton Formation to the northeast (King and Ferguson, 1960; Brown and Spencer, 1981; Rankin, 1993). The formation unconformably overlies the rocks of the Blue Ridge basement complex and possibly the Catoctin Formation in western Amherst County and is disconformable with the underlying Konnarock Formation in Grayson County. The upper unit is generally 600 to 1000 feet thick and the lower unit ranges from less than 100 feet to more than 1500 feet.

Maccrady Shale (Mississippian) at surface, covers 0.2 % of this area

Maccrady Shale (Stose, 1913). Shale, siltstone, minor limestone, and sandstone. Shale and siltstone, light-grayish red, few light-greenish-gray beds, silty, very-thin- to medium bedded, indistinctly bedded, interbedded. Collapse breccia in middle of formation, with anhydrite (?) locally in western Tazewell County (Windolph, 1987). Limestone, dolomitic, light-yel lowish-brown and bluish-gray in Washington and Tazewell counties. Sandstone, light- to medium-gray, fine to coarse-grained, locally cross-bedded. Maccrady sparsely fossiliferous including a fish-bone bed (Bartlett, 1974, p. 101). Contains salt, anhydrite, and economic deposits of gypsum where the formation is thickest and folded and faulted in Smyth County (Sharpe, 1984; Stose, 1913). Basal beds locally interfinger with and are gradational with underlying Price Formation and lie on progressively older units of the Price west of a line from north astern Tazewell County through central Washington County (Bartlett, 1974, p. 99). Maccrady thins northwestward, but locally thins southwestward (Warne, 1990). It wedges out at the southwest corner of Virginia (Englund, 1979); in northern and western Washington and northwestern Smyth counties the Maccrady is less than 50 feet thick (Averitt, 1941; Warne, 1990), but it is as much as 2000 feet thick to the northeast in Smyth County (Sharpe, 1984), and at least 1000 feet thick in a partial section in Montgomery County (Bartholomew and Lowry, 1979).

Ashe Formation - Biotite gneiss (Proterozoic Z) at surface, covers < 0.1 % of this area

Medium- to light-gray, massive, conglomeratic biotite schist and gneiss, with feldspar, quartz, and granitic clasts; grades upwards into medium- to fine-grained, salt-and-pepper-textured two-mica plagioclase gneiss with very-light-gray mica schist interbeds. Quartzite, impure marble, calcareous gneiss and amphibolite occur locally. Some dark-gray to black, pyrite-bearing mica schist occurs at tops of thick, fining-upwards graded sequences. Mineralogy: (1) quartz + plagioclase + potassium feldspar + biotite + muscovite + chlorite + epidote + ilmenite; (2) quartz + plagioclase + biotite + muscovite + epidote-allanite + garnet + titanite + ilmenite; (3) quartz + calcite + plagioclase + biotite + muscovite + epidote + ilmenite + titanite; chlorite occurs as a secondary mineral. Unit is unconformable on Grenville basement and cut by Late Precambrian mafic and felsic dikes.

Elk Park Plutonic Group - Biotite augen gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Elk Park Plutonic Group (Yep, Yec; Rankin and others, 1972; 1973) Includes augen gneiss and porphyritic gneiss (Yep), and equigranular quartz monzonite, quartz monzonite flaser gneiss, and quartz monzonite gneiss (Yec). Rocks range in composition from diorite to quartz monzonite; most are quartz monzonite in which the primary dark mineral is biotite, with or without hornblende; epidote and titanite are common accessory minerals. Porphyritic rocks contain microcline phenocrysts. Augen gneiss was probably derived from porphyritic plutonic rocks by shearing. This unit includes in part the Little River Gneiss of Dietrich (1959) and Cranberry Gneiss (Rankin and others, 1972; 1973). U-Pb zircon data from the Cranberry has been interpreted to signify ages of 1050 Ma (Davis and others, 1962) and 1080 Ma (Rankin and others, 1969).

Lower Ordovician and Upper Cambrian Formations Undivided (Cambrian-Ordovician) at surface, covers < 0.1 % of this area

Includes Pinesburg Station Dolomite, Rockdale Run Formation, Beekmantown Formation, Stonehenge Limestone, and Conococheague Formation. Refer to descriptions under Ob and O[co/[co.