Field mapping, structural analysis, and mineral equilibria of rocks between Fries and Galax, Virginia provide information on the tectonic and metamorphic history of the Ashe Formation, a series of late Precambrian gneisses, pelitic schists and amphibolites, and the underlying Cranberry Gneiss. The dominant penetrative foliation of the rocks is composed of an early S₁ foliation that is crenulated and transposed by a later S₂ foliation which strikes N 50° E and dips SE. Metamorphic porphyroblast growth of biotite, garnet, staurolite, and kyanite followed penetrative foliation development, with metamorphic grade increasing stratigraphically upward to form inverted isograds. Thrust faulting along the Fries Fault caused extensive mylonitization of the Cranberry Gneiss and offset of the metamorphic isograds. Textural evidence indicates that mylonitization is the greatest in rocks at the Fries Fault trace, and decreases upward through the Cranberry-Ashe contact. No textural evidence of an additional episode of faulting at the AsheCranberry contact was observed, based on lack of a second episode of mylonite, relatively good preservation of sedimentary clasts in the Ashe, and similarity of metamorphic grade. Mineral equilibria show systematic trends from chlorite-biotite grade to staurolite-kyanite grade. Muscovite compositions show an increase in paragonite component and decrease in celadonite component. Chlorite, biotite, garnet, and staurolite show a systematic increase in Mg/(Mg+ Fe) toward higher grade. AFM topologies indicate that these compositional trends may be explained a series of continuous reactions ( chl + mu=bi + q + V followed by chl + mu + q=gt + bi + V) and discontinuous reactions (gt + chl + mu= st + bi + V followed by st + chl + mu= ky + bi + V). Temperatures inferred from garnet-biotite equilibria are approximately 550 to 600° C in the staurolite zone, with pressures estimated from various equilibria to be between 4.5-7 kb. The inversion of the isograds is interpreted as resulting from overthrusting of the Ashe metasediments during the Paleozoic. The above information can also be applied to the deformation of the Gossan Lead massive sulfide. Structural data from the Bumbarger mine pit indicates that the massive sulfide underwent the same sequence of structural events as the surrounding rocks. During D₂, shearing of gneisses and schists in a matrix of ductile pyrrhotite caused isoclinal folding, fracture, and rotation of the metasediments while preserving the gross sedimentary layering. This information confirms synsedimentary models of the formation of the Gossan Lead. / Ph. D.

The Saltville-Broadford area is largely on the northwestern limb of the Greendale syncline in the Valley and Ridge Province of Virginia. The area mapped covers 12 square miles of the northwest corner of Smyth County, Virginia. The rocks in the area ranging in age from Cambrian to Mississippian are found in three different structural settings, the hanging wall and footwall of the Saltville fault, and in two thrust slices located along the trace of the Saltville fault. The hanging wall consists of the Honaker Dolomite of Cambrian age and younger rocks outside the map area. The footwall consists of the Price Sandstone, Maccrady Shale and Little Valley Limestone all of Mississippian age and older rocks outside the map area. The larger of the two slices consists of an overturned sequence of the Juniata Sandstone of Ordovician age to the Brallier Formation of Devonian age. The smaller slice consists of undifferentiated Devonian shale. The Saltville fault, a low-angle thrust, has overturned and cut off the southeastern limb of the Greendale syncline. During thrusting, two slices, at least one of which is overturned, were carried with the overriding block to their present positions. A total of 12,500 feet of movement was measured where the Cambrian, Honaker Dolomite is in fault contact with the Mississippian Little Valley Limestone. Total movement of the fault is believed to be of the order of 4 miles. The upper part of the Mississippian Maccrady Formation is a sequence of evaporites. Halite and gypsum constitute the chief economy of the Saltville area. / M.S.

The Big Walker Mountain-Crockett Cove area lies in the Valley and Ridge province of southwestern Virginia and is made up of Middle Cambrian-Lower Mississippian strata which are exposed in two separate northeast-trending strike belts. The area is bounded on the northwest by the northwestern limb of the Greendale syncline which has been overridden from the southeast by rocks of the Saltville block. The northeast-trending Saltville thrust probably dips less than 25° in the area near Bland, Virginia, where Middle Ordovician rocks are exposed in a fenster. The rocks exposed in the fenster are probably part of the northwest limb or near-trough portion of the Greendale syncline. The major structure of the Saltville block is the walker Mountain homocline which has subsidiary folds that plunge eastward into a much larger structure - the Blacksburg synclinorium - which is located just east of the area studied. The Saltville block is broken at its southern limit in most of the area by the Tract Mountain reverse fault which essentially parallels the trace of the Saltville fault. Stratigraphic displacement along the Tract Mountain fault decreases from a maximum of about 8,000 feet near its southwestern terminus where the Pulaski block overrides it from the south,to less than 1,000 feet nearly 18 miles away at the eastern border of the area studied. The Tract Mountain block, which is bounded on the northwest by the Tract Mountain fault, is made up of a series of northeast-trending folds which plunge eastward toward the Blacksburg synclinorium. Mapping of the Tract Mountain block and stratigraphic studies of two of its larger folds, the Crockett Cove anticline and the adjacent Queens Knob syncline, show that there is no appreciable thickness or lithologic change in Middle Cambrian-Lower Ordovician rocks between syncline and anticline. However, the basal Champlainian Series in the more southern fold, the Queens Knob syncline, has an aggregate thickness of about 4,400 feet, whereas the same interval near the crest of the Crockett Cove anticline is less than 2,000 feet thick. Most of the beds present near the trough of the syncline are markedly more clastic and less pure than the corresponding beds on the crest of the adjacent anticline which is less than 2.5 miles up structure to the north. Based on this evidence, it is concluded that the present structural axes are identical to axes of maximum and minimum differential subsidence of the sea floor during Middle Ordovician-Late Silurian time. The synclinal trough was the site of maximum subsidence and the anticlinal axis was the site of minimum subsidence. The date of inception of these two folds must correspond to the beginning of pronounced vertical movement of the sea floor which started in early Champlainian time. The anticline which must have at one time lay adjacent to and southeast of the Queens Knob syncline was probably eliminated as a large fault slice during movement along the Pulaski fault that strikes obliquely across the axis of the Queens Knob syncline, which is the southernmost structural element of the Tract Mountain block. The leading edge of the Pulaski block forms the southern border of the Big walker Mountain-Crockett Cove area.which contains approximately 160 square miles that was mapped on a scale of 2 inches to the mile. / Ph. D.

In the Middle Ordovician strata of southwestern Virginia, a distinctive succession of yellow-drab and gray mudstones, shales, and limestones occurs between the overlying Martinsburg formation and the underlying red Moccasin formation. For many years, part of this succession was classified with the Martinsburg formation and part with the Moccasin formation. This practice could not be condemned on faunal grounds because the fauna of the sequence between the Moccasin and Martinsburg is so sparse and equivocal in general character. Altered volcanic ash beds which are especially characteristic of the succession range as low as the middle part of the Moccasin formation and are also present in the lower Martinsburg formation. Mathews (1934, p.48) proposed the name, Eggleston, and defined it to include the relatively unfossiliferous transitional beds and intercalated bentonites younger than the upper maroon Moccasin formation and older than the Trenton beds of the lower Martinsburg formation in Giles County, Virginia. Until the present study was undertaken, few detailed studies of the Eggleston, as a separate unit, had been made. The almost barren beds had drama little or no interest from the paleontologist. The intercalated bentonites were studied, only as a part of the Moccasin-Martinsburg succession, and an attempt was made to correlate these related beds with similar beds in other localities. The name, Eggleston, has been accepted and is used in much of the literature published since 1935 but no attempt has been made to correlate the entire succession of beds lying between the Moccasin and Martinsburg formations with similar succession throughout southwestern Virginia. The writer has made a detailed study of this succession between New River and the Tennessee line to determine the relationship of faunas to the intercalated bentonites, and to correlate the beds of the succession with those at other localities in southwestern Virginia. / Master of Science

Marine sedimentary rocks ranging in age from Early Cambrian(?) to Middle Ordovician, inclusive, crop out in the Damascus area. Approximately 13,000 feet of beds are exposed, comprising 14 formations. The stratigraphic succession is rather complete and is broken by a single recognizable hiatus which represents most of late Early Ordovician time. Clastic rocks of questionable Early Cambrian age are about 3,600 feet thick. Rocks of known Cambrian age are about 6,800 feet thick and consist of, in ascending order, elastic rocks, dolomite, shale and carbonate rocks, and mixed carbonate rocks. Carbonate rocks of Early Orodovician age range from 1,000 to 6,000 feet in thickness. Middle Ordovician rocks aggregate approximately 800 feet in thickness, the basal 100 feet of which is limestone and the remainder is shale and sandstone. The Elbrook formation of middle and Late Cambrian age is herein divided into four members of which one, the Widener limestone member, is formally named and mapped. A crepicephalus fauna from the Widener limestone, and a single trilobite, Plethometopus sp. From the Conococheague formation are illustrated. The strata have been folded into five synclines and four anticlines and are broken by two major thrust faults, and Lodi thrust and the Holston Mountain thrust. The faults were initially low-angle thrusts which have been folded with the overridden rocks so that locally the fault planes have steep dips. / Master of Science

The conclusion of this investigation, based on field mapping and measured sections, is the Price Formation was deposited on a high-energy shoreline. Sediments for the shoreline were initially transported from a northern deltaic source. The Cloyd Conglomerate Member represents offshore barrier bars, while the Lower Price unit was deposited in a lagoon behind the bars. At the top of the Lower Price unit, the "marker bed" sandstone includes sedimentary features of marine and fluvial origin. This sandstone is interpreted as a delta-front sand, reworked from distributary mouth bars. The Langhorn and Merrimac coal seams were deposited in swamps formed across the sandstone. / Master of Science

The western boundary of the Charlotte Belt near Brookneal, Virginia lies midway along a 100 km length of the boundary previously mapped by reconnaissance methods only (Jonas, 1928). This study concludes that the metavolcanic Chopawamsic Formation of northern and central Virginia is the extension of the Charlotte Belt. The Charlotte Belt is bounded to the west by the metasedimentary Evington Group that extends from northern Virginia southward into the Smith River Allochthon as the Fork Mountain Schist. In Brookneal, the boundary between the eastern metavolcanic and western metasedimentary units is obscured by the intrusion of the 470 Ma Melrose Granite. The abrupt change in lithology and multiple fault generation across the granite indicates that the boundary between the metasedimentary and metavolcanic units is tectonic. Unconformably overlying both the metavolcanic and metasedimentary units is the Arvonia sequence, previously not documented in the southern Virginia Piedmont. The Brookneal terrane has undergone three metamorphic events and localized hydrothermal retrogression. The metamorphism is tied in sequence to seven folding episodes. The metamorphism and deformation are results of the regional Taconic event, the late-Acadian event which terminates to the west in Brookneal, and the fault localized Alleghanian event, each of which resulted in faulting. / Master of Science

The Knox unconformity in the central and southern Appalachians is developed on Lower to early Middle Ordovician Knox/Beekmantown carbonates. The unconformity marks the transition from Cambro-Ordovician shelf carbonate deposition on a passive margin to carbonate and clastic deposition in a foreland basin associated with a convergent margin, possibly during a time of global sea-level lowering. Erosional relief on the unconformity decreases from over 140 m in southwest Virginia to 20 m or less in northern Virginia. This corresponds with a marked decrease in stratigraphic relief in the same direction. Paleokarst features that formed on the unconformity include topographic highs that extend up to 30 m into overlying Middle Ordovician peritidal carbonates, sinkholes and caves that extend down to 65 m below the unconformity and are filled with detritus from the unconformity and breccia from host carbonates, and sub-unconformity dolomite breccia bodies that formed by collapse after dissolution of limestone interbeds. Coarse detritus on the unconformity surface formed thin to thick veneers of regolith; locally this material was reworked by fluvial and marine processes. Much fine dolomite detritus was reworked and deposited as alluvial fan and playa mud-flat sediments in lows on the unconformity surface. The unconformity influenced the regional distribution, composition and thickness of some post-unconformity peritidal carbonates. This is evidenced by lithoclastic supratidal sheets that cap cycles in these beds up to 100 m above the unconformity. Unconformity highs also may have controlled later Middle Ordovician buildup distribution in Virginia. Development of regional unconformities on shelf sequences of passive margins immediately beneath foreland basin sequences is common in other orogens, reflecting gentle warping of the shelf prior to foundering beneath synorogenic clastics. Such unconformities may localize hydrocarbons and base metal deposits (Pb-Zn), by controlling the distribution of permeable horizons adjacent to the unconformity. / Master of Science

Drill cores through the Lower to Middle Cambrian Shady Dolomite carbonate platform (600 to 1200 m thick) in the Austinville, Virginia, region allow the evolution of the carbonate platform from a gently sloping ramp, to a high relief, rimmed shelf to be documented. The Shady Dolomite forms the initial carbonate foundation for the overlying Cambrian-Ordovician carbonate shelf sequence, which persisted for about 30 m.a. until it was destroyed by incipient collision during the Early Ordovician. The Shady Dolomite records several episodes of dolomitization during burial, coeval with late Paleozoic deformation. Rare relict corcs of zone 1 dolomite were replaced and overgrown by zone 2A dolomite, the dominant replacement phase. After replacement dolomitization, the sequence was subjected to dissolution and fracturing, followed by Pb-Zn mineralization, zones 2B, 3 and 4 dolomite cement, sphalerite, quartz, and calcite. Zone 1 dolomite apparently has similar isotopic and trace element composition as zone 2A dolomite. Zone 2A dolomite (δ¹⁸O = -10.2 to -7.0 °/oo PDB; δ¹³C = +1.0 to +1.6 °/oo PDB) is depleted in ¹⁸O and enriched in ¹³C relative to marine cements (δ¹⁸O = -7.5 to -6.1; δ¹³C = +0.2 to +0.8), reflecting precipitation at elevated temperatures from fluids in equilibrium with the host limestone. Zone 2B dolomite cement has identical δ¹⁸O values as zone 2A dolomite, indicating precipitation from similar fluids for the two dolomite generations. The Mn and Fe contents of zones 2A and 2B dolomite likely reflect a pH control over the fluid Mn and Fe chemistry; their similar low total Sr and nonradiogenic ⁸⁷Sr/⁸⁶Sr, imply that Sr was largely derived from the limestone precursor. Zones 3 and 4 dolomite cements (δ¹⁸O = -13.8 to -11.3; δ¹³C = -0.7 to +0.9) are depleted in δ¹⁸O relative to previous dolomites, recording hotter fluids. Zone 3 dolomite is depleted in Fe, due to pyrite precipitation whereas zone 4 dolomite cement has relatively high Mn and Fe contents. Zones 3 and 4 dolomite cements and later calcite are enriched in total Sr and have high ⁸⁷Sr/⁸⁶Sr, indicating late radiogenic Sr-enriched brines. Fluid inclusions indicate that zones 2A and 2B dolomite precipitated from warm (100-175°C), saline (23-26 wt.% NaC1 equiv.) fluids, followed by later hotter (175-225°C) more saline (30-33 wt.% NaCl equiv.) fluids. Pressure solution of the Knox Group dolomites during overthrusting provided much of the Mg²⁺ for dolomitization, this Mg²⁺ was transported by regional gravity-driven fluid flow that developed in response to tectonic uplift. / Ph. D.

Ground-water geology along the northwest foot of the Blue Ridge between Arnold Valley and Elkton, Virginia The area discussed in this report lies along the northwest flank of the Blue Ridge in Rockbridge, Augusta, and Rockingham counties, Virginia. It spans the boundary between the Blue Ridge and the Great Valley physiographic provinces. The southeastern (Blue Ridge) portion of the area is mountainous and underlain by Precambrian crystalline and lower Cambrian elastic rocks. It is a major water catchment area for the eastern edge of the Shenandoah Valley and is chiefly a National Forest preserve. Cambriancarbonate rocks and fine-grained elastics underlie the relatively level areas between the mountains and the major subsequent streams near their base. A thick unconsolidated mantle which slopes gently away from the mountains conceals bedrock over much of the area. Major well fields have been developed on level alluvial floodplains and terraces adjacent to the rivers. Some produce several million gallons of water each day from bedrock aquifers at depth of from 50 to over 700 feet. The average temperature within the area is about 55°F. Average annual precipitation is approximately 41 inches and is greatest in the mountains. About six inches becomes ground-water recharge. Artificial withdrawal by wells would increase the rate of recharge. Evapotranspiration frequently exceeds total precipitation during the summer and early autumn. Most streams which drain the Blue Ridge are perennial near the headwaters and intermittent northwest of the mountains. They may be influent to bedrock aquifers within or near the base of the mountains and near the confluence with subsequent streams where the clay mantle is deeply eroded, but are effluent in the intervening reaches. The perennial streams are dominantly effluent. The major rivers are sub•sequent and effluent. They receive surface drainage and overflow of ground-water reservoirs from the Blue Ridge and from dominantly carbonate terranes to the west and northwest. Streamflow of the major streams represents approximately one third of the average annual areal precipitation. The stratigraphic sequence within the area from older to younger is designated as fellows: Precambrian crystalline rocks; Precambrian-Lower Cambrian Catoctin Greenstone and Swift Run Formations; LowerCambrian elastics; Lower Cambrian Tomstown (Shady) Delomite; Lower Cambrian Waynesboro (Rome) Formation; Middle Cambrian Elbrook Formation; and the Upper Cambrian Conococheague Limestone. The Precambrian igneous and metamorphic rocks, and the lower portion of the Lower Cambrian elastics are normally relatively poor aquifers. Minor production is obtained from fractured zones at locations within the mountains. The Antietam formation, the upper portion of the Lower Cambrianelastics, is a major potential aquifer. One well in Buena Vista produces over 600 gpm of water of low mineralization. Similar sites abound along the base of the Blue Ridge. The Tomstown Dolomite is a major aquifer at Waynesboro where the DuPont well field produces over 11,000,000 gpd. The producing characteristics of the Tomstown formation near the mountains at locations remote from the major rivers, where it is commonly concealed by a thick impermeable mantle of clay, are virtually unknown. Thick beds of limestone and dolomite in the Waynesboro Formationare prolific aquifers at Glasgow and near Elkton. Argillaceous portions of the formation are commonly aquicludes although secondary permeability may be developed by fracturing. Several wells produce over 1000 gpm from aquifers in the Elbrookand Conococheague formations near Grottoes and south of Elkton. With some exceptions, the water produced from these formations is harder than that produced from older formations to the east. A mantle of Cenozoic gravel and clay up to 400 feet thick overlies the bedrock over wide areas. The lower portion consists primarily of silty clay which is largely residual. Near the base of the mountains where it is thickest. it consists largely of leached colluvial material derived from the adjacent formations. It is characteristically an aquiclude which inhibits direct downward percolation of water to the underlying bedrock. Water encountered in the bedrock below it is commonly under mild artesian head. The upper portion of the mantle consists dominantly of alluvial and colluvial gravel with a sandy clay matrix and discontinuous beds of sand or of sandy or silty clay. It lies unconformably over residual clay and bedrock and is probably of Pleistocene age. It grades into talus near the foot of the mountains. The Cenozoic mantle yields only small amounts of water of variable quality to domestic wells although several large springs issue from it. The structural geology of the area is complex. Interpretation is complicated by facies changes and poor exposure. Fractures produced by deformation of the brittle rocks provide permeability. The main effect of the structure is its effect on the distribution of potential aquifers. The occurrence of ground water within the area is probably influenced more by topography, distribution of the unconsolidated mantle, and lithologic characteristics of the bedrock than by structure. Calcium and magnesium bicarbonate is the principal chemical constituents of ground water produced from major wells and springs within the area. Water from the carbonate aquifers is commonly moderately hard (61-120 ppm as CaC03). Nearly all of the hardness is temporary(carbonate) and is approximately equivalent to the alkalinity. Concentrations of deleterious substances are low. Water from the elastic rocks is characterized of low mineralization and pH. It is corrosive to ferrous metals. The temperature of well waters varies from 12° to 15°c. (54° - 59°F.)with few exceptions. Quality of ground water can commonly be correlated with the geologic formation from which it is produced. The concentration of total dissolved solids in waters from the bedrock aquifers tends to increase with decreasing age of the aquifer and with distance from the mountains. Water from limestone is commonly more highly mineralized than that from dolomite. Waters from. the same formation tends to be more highly mineralized west of the major rivers than they are to the east. Mineralization of most of the waters studied is derived from the dissolution of the carbonate aquifers and is controlled by equilibrium relations between dolomite, calcite, and dissolved carbon dioxide. The degree of saturation of waters with respect to solid calcite and dolomite can be determined semiquantitatively by comparison of the equilibrium pH computed from water analyses with the measured pH. Waters from typical dolomite reservoirs are supersaturated with respect to dolomite. The ratio of the concentration of calcium to the concentration of magnesium of most samples reflects the composition of the reservoir rock. Most samples contain more calcium than magnesium. Relationships between the calcium-magnesium ratio, the total mineralization, and the degree of saturation of water samples with respect to the solid carbonates are useful to relate the geology of the area to its hydrology. The quality of river water fluctuates widely with meteorologic variations, but that of ground-water produced from bedrock in adjacent wells east of the river remains relatively constant. Recharge to the wells at depth is evidently sufficient to prevent downward percolation of appreciable quantities of surface flow into the good bores although pumping levels are commonly below river level. The quality of the water suggests that recharge is dominantly from the east. Dolomite aquifers underlying floodplain and terrace deposits east of the major rivers are most favorable for the industrial development of ground-water resources. Prospective areas are outlined. Wells located in minor stream valleys near the boundary between the Blue Ridge and the Valley also offers prospects of production from Antietam or Tomstownaquifers. Test-drilling is warranted. Drilling of test wells should be the first step of industrial site investigation. The location of wells should be based upon a detailed local surface geological investigation. / Doctor of Philosophy