Geologic units in Smyth county, Virginia

Additional scientific data in this geographic area

Erwin and Hampton Formations (Cambrian) at surface, covers 14 % 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.

Shady Dolomite (Cambrian) at surface, covers 11 % 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).

Rome Formation (Cambrian) at surface, covers 8 % 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.

Knox Group (Cambrian-Ordovician) at surface, covers 8 % 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.

Elbrook Formation (Cambrian) at surface, covers 7 % 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).

Silurian Formations Undivided (Silurian) at surface, covers 6 % of this area

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

Maccrady Shale and Price Formation (Mississippian) at surface, covers 5 % of this area

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

Nolichucky and Honaker Formations (Cambrian) at surface, covers 5 % 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.

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.

Moccasin or Bays Formation through Blackford Formation (Ordovician) at surface, covers 5 % 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 4 % 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.

Unicoi Formation (Cambrian) at surface, covers 4 % 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.

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).

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.

Beekmantown Group (Ordovician) at surface, covers 2 % 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.

Konnarock Formation (Proterozoic Z) at surface, covers 2 % of this area

Konnarock Formation (Rankin, 1993). Mostly moderate-red glaciogenic sedimentary rocks include massive diamictite (tillite), bedded diamictite, varve-like laminite locally containing dropstones, massive mudstone, pink arkose, and minor conglomerate. Clasts in the diamictite and laminite are dominantly granitoid, but include rhyolite and greenstone of the Mount Rogers Formation. Thickness is as much as 3275 feet; diamictite is most common toward the top of the section.

Chepultepec and Copper Ridge Formations (Cambrian-Ordovician) at surface, covers 1 % of this area

Chepultepec Formation (Ulrich, 1911). Dolostone, argillaceous, sandy, light-gray, light-olive-gray, and grayish-brown,very-fine- to coarse-grained. Contains white to light-gray chert nodules and beds; sandstone and dolomitic sand stone lenses and beds; scattered sand grains; minor intraformational conglomerate beds; greenish-gray clay shale partings; and dark-gray, petroliferous dolostone. The Chepultepec ranges from 300 to 850 feet in thick ness (Brent, 1963). Copper Ridge Formation (Ulrich, 1911). Dolostone, generally divisible into a lower olive-brownish-gray to darkgray, medium- to coarse-grained, thick- to massive-bedded dolostone, some of which emits a petroliferous odor on freshly broken surfaces ("stinkstone"); and an upper olive-brownish- gray to light-gray, very-fine- to medium-grained dolostone with minor silty and sandy zones. Olive-black, oolitic chert beds and light-gray to white, chalcedonic chert nodules are present. Similar divisions were described by several geologists including Miller and Brosgé (1954), Miller and Fuller (1954), and Bridge (1956). The Copper Ridge ranges from 415 to 850 feet in thickness. Maynardville Formation (Oder, 1934). Limestone and dolostone. Limestone, locally dolomitic, locally argillaceous, medium- to dark-gray, very-fine- to fine-grained, medium- to thick-bedded, mottled; with argillaceous to dolomitic bands and partings which give the rock a ribbon-banded or straticulate appearance. Dolostone, very-light-gray to dark-gray, light-olive-gray to olive-gray and locally yel low ish-gray or dark-bluish-gray, very-fine- to coarse-grained, finely laminated to thick-bedded (thin-bedded near top of unit distinguishes it from overlying Copper Ridge Formation); with black chert; minor lenses and beds of fi ne- to medium-grained, locally dolomitic sandstone; very-fine-grained, yellowish-gray, argillaceous sand stone; and rounded-pebble conglomerate; all locally present. Generally the limestone is in the lower one third to one-half of the unit and the dolostone is in the upper two-thirds to one-half of the unit, with a transition zone from one to the other. The Maynardville Formation ranges from 60 to 300 feet in thickness, thinning to the east-northeast from Lee County. Thickness variations may be due in part to grouping of the limestone with the underlying Nolichucky Formation or the dolostone with the overlying Copper Ridge, as noted by Derby (1965).

Mount Rogers Formation - Phenocryst-poor rhyolite (Proterozoic Z) at surface, covers 1 % of this area

Phenocryst-poor rhyolite (Whitetop Rhyolite Member and Buzzard Rock Member, Mt. Rogers volcanic center). Whitetop Rhyolite Member, phenocryst-poor, very dusky purple, high-silica, metaluminous rhyolite lava fl ows and minor tuff containing 0 to 10 percent phenocrysts of quartz and mesoperthite. Buzzard Rock Member, blackish-red, low-silica, metaluminous rhyolite lava flows containing 5 to 20 percent prominant phenocrysts of mesoperthite and plagioclase; includes minor interbedded volcaniclastic sedimentary rocks. The Buzzard Rock is a thin unit that occurs beneath the Whitetop Rhyolite Member.

Greenbrier Limestone (Mississippian) at surface, covers 0.5 % of this area

Greenbrier Limestone (Rogers, in Macfarlane, 1879). Limestone, dolomite, and minor shale. Limestone, very-light olive-to olive-gray and brownish-gray, and medium- to dark gray, micrograined to coarse-grained, thin- to thick- bedded, thinner bedded in upper part, even- to cross-bedded; few shaly beds in upper part; oolitic in upper part and in cross-laminated beds near base; black chert near middle of formation, gray to pale-red near base; very fossiliferous. Pale-brown dolomite near upper chert zone, minor dolomite locally in lower part. Few interbeds of greenish-gray and grayish-red, calcareous, silty shale. Limestone is petroliferous locally in upper part (Henika, 1988). Base locally unconformable with underlying Maccrady Shale. Formation thickens to east, ranging from 200 feet in western Wise County to 3500 feet in Washington nd Scott counties. The Greenbrier is equivalent to (descending): Gasper Limestone, Ste. Genevieve Limestone, St. Louis Limestone (Hillsdale Limestone), and Little Valley Limestone (Warsaw equivalent), and to lower part of the Newman Limestone (Butts, 1940; LeVan and Rader, 1983). Newman Limestone (Campbell, 1893). Limestone and shale. Limestone, light-olive-gray in lower half, medium-gray to olive-gray in upper half, aphanic to fine-grained, partly oolitic, partly argillaceous, with basal beds of dark-gray chert nodules and local dolomite. Shale, medium-gray to medium dark-gray, partly calcareous, interbedded with limestone in upper half of unit. The Newman Limestone ranges from 550 to 600 feet in thickness and is equivalent to the Bluefield Formation and Greenbrier Limestone. Fort Payne Chert. (Smith, in Squire, 1890). Greenish gray chert in thin beds (2 - 6 inches thick); with shale partings. The Fort Payne Chert ranges from 0 to 20 feet in thickness and pinches out to the northeast. Grainger Formation (Campbell, 1893). Shale, pale-olive or greenish-gray to dark-greenish-gray, locally gray ish-red in lower half and at top; with some interbedded pale-olive-gray siltstone and very-fine-grained sandstone, locally abundant siderite nodules near base. The Grainger Formation ranges from 250 to 325 feet in thickness and is the lateral equivalent of the Maccrady Shale and Price Formation.

Mount Rogers Formation - Greenstone with interbedded sedimentary rocks (Proterozoic Z) at surface, covers 0.2 % of this area

Greenstone with interbedded sedimentary rocks; relict plagioclase phenocrysts are prominent in some greenstone.

Mount Rogers Formation - Porphyritic rhyolite (Proterozoic Z) at surface, covers 0.2 % of this area

Porphyritic rhyolite (Wilburn Rhyolite Member, Mt. Rogers volcanic center). Very-dusky-purple, high-silica rhyolitic welded tuff containing about 30 percent quartz and mesoperthite phenocrysts. This unit constitutes a chemically and mineralogically-zoned ash-flow sheet at least 760 m thick, in which the main body is metaluminous and the basal phenocryst-poor 30 m were initially peralkaline.

Lower Devonian and Silurian Formations Undivided (Silurian-Devonian) at surface, covers < 0.1 % of this area

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

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).

Chilhowee Group (Cambrian) at surface, covers < 0.1 % of this area

Chilhowee Group (Keith, 1903). The Chilhowee Group includes the Antietam, Harpers, and Weverton Formations in the northeastern portion of the Blue Ridge Province and the Erwin, Hampton, and Unicoi Formations in the southwestern portion of the Blue Ridge Province. Antietam Formation (Williams and Clark, 1893). Quartzite, medium-gray to pale-yellowish-white, fine- to medium grained, locally with very minor quartz-pebble conglomerate, cross-laminated, medium- to very-thick-bedded, very resistant, forms prominent cliffs and ledges, contains a few thin interbeds of light-gray phyllite, has calcareous quartz sandstone at the top that is transitional with the overlying Tomstown Dolomite, and many beds contain Skolithos linearras. It is laterally equivalent to the Erwin Formation to the southwest. The formation interfingers with the underlying Harpers Formation and ranges in thickness from less than 500 feet in Clarke County to nearly 1000 feet in Rockingham County (Gathright and Nystrom, 1974; Gathright, 1976). Harpers Formation (Keith, 1894). Metasandstone, metasiltstone, and phyllite. Metasandstone, dark-greenish gray to brownish-gray, fine-grained, sericitic, thin- to medium-planar bedded, locally bioturbated, Skolithos-bearing litharenite; dark-gray, fine-grained, cross-laminated, thickbedded, laterally extensive bodies of quartzite; and very-dark gray, medium- to coarse-grained, thick-bedded, ferruginous, very resistant, quartzitic sandstone. These beds were extensively mined for iron ore north of Roanoke (Henika, 1981). Metasiltstone, dark-greenish-gray, thin, even bedded, sericitic, and locally bioturbated. Phyllite, medium- to light-greenish gray, bronze weathering, laminated, sericitic. The Harpers is laterally equivalent to the Hampton Formation to the southwest and they are so similar that the names have been used interchaneably in the northern Blue Ridge (Gathright, 1976; Brown and Spencer, 1981). The Harpers conformably overlies the Weverton or Unicoi Formations, thickens northeastward from about 1500 feet north of Roanoke to about 2500 feet in Clarke County. The thicker sections are dominated by phyllite and metasiltstone and the thinner sections by metasandstone and quartzite. Weverton Formation (Williams and Clark, 1893). Quartzite, metasandstone, and phyllite. Quartzite, medium- to very dark-gray, weathers light-gray, fine- to coarse-grained, well rounded quartz-pebble conglomerate beds locally, medium- to thick-bedded, cross-bedded, very resistant, with interbedded metasandstone, dark-greenish- gray, feldspathic, thick-bedded, with ferruginous cement in some beds. Phyllite, light- to dark-greenish-gray or dark-reddish-gray, laminated, sericitic, with coarse sand grains and quartz-pebble conglomerate in a few thin beds, generally in lower part. Formation ranges in thickness from more than 600 feet in Clarke County to less than 200 feet in Augusta County (Gathright and Nystrom, 1974; Gathright and others, 1977). The Weverton is lithologically very similar to strata in the upper portion of the Unicoi Formation to the south to which it may be equivalent. The Weverton appears to unconformably overlie the Catoctin and Swift Run Formations and the Blue Ridge basement complex and is present northeast of Augusta County.