The titanium deposits of Nelson and Amherst counties, Virginia, occur in Precambrian (?) rocks that constitute part of the core of the Blue Ridge-Catoctin Mountain anticlinorium. Approximately 72 square miles were mapped in this study. The central part of the mapped area is underlain by a mass of pegmatitic anorthosite, about which other mappable rock units are distributed more or less peripherally. The chief units, listed from oldest to youngest, are: augen gneiss, biotite pencil gneiss, biotite aplitic gneiss, granitic gneiss, feldspathic gneiss, hypersthene granodiorite, pegmatitic anorthosite, and nelsonite. The pegmatitic anorthosite occurs as sills and dike-like bodies. It originally consisted of coarse-grained, antiperthitic plagioclase (An₃₀). Most of the primary textures in this rock have been obliterated by alteration so that the present rock consists of saussuritized feldspar and minor amounts of altered mafic minerals, plus introduced or recrystallized quartz, rutile, and ilmenite. The mafic minerals include tremolite or anthophyllite, in complete or partial pseudomorphs after coarse-grained pyroxene crystals, and abundant alteration halos of biotite and chlorite. Most of the rocks have a well developed, generally northeasterly striking, southeasterly dipping gneissosity. The rocks were deformed prior to and after alteration and mineralization. Layered structures in hypersthene granodiorite suggest that the rocks have a domal arrangement. A low angle fault in the northeast part of the mapped area apparently resulted in thrusting of the augen gneiss over part of the pegmatitic anorthosite. Most of the rock types are believed to be of igneous origin, although the augen gneiss may be all or in part metasedimentary. The pegmatitic anorthosite and the hypersthene bearing rocks are believed to be comagmatic. Most of the titanium occurs as ilmenite in ilmenite nelsonite bodies and disseminated in highly altered rocks adjacent to the pegmatitic anorthosite. Lesser amounts of rutile occur disseminated in relatively pure but altered pegmatitic anorthosite, in rutile nelsonite end in rutile-bearing quartz veins. The titanium deposits are associated with zones of intense alteration characterized by the development of chlorite, biotite, and amphiboles from mafic minerals in the wall rock, and by saussuritization of the feldspars. Evidence indicates that most or all of the deposits formed by replacement of the wall rock. Titanium, fluorine, phosphorus, water and minor carbon dioxide were added to the wall rocks during alteration and mineralization. The iron-titanium. ratio increases outwardly from the central pegmatitic anorthosite. The original mineralizing fluids may have acquired iron from alteration of the wall rocks. Although the mineralizing fluids may have been derived by differentiation of the same magma from which the hypersthene granodiorite and pragmatic anorthosite were derived, the mineralization was later than the crystallization of the relatively titanium-rich wall rocks. The purer pegmatitic anorthosite is quarried and ground principally for use in the glass industry. Reserves are probably large, but the discontinuity of the pure feldspar rock units demands that each prospective quarry site be drilled thoroughly to determine the quality and extent of the feldspar. A conservative estimate places the reserves of TiO₂ at approximately 12 million tons. Only weathered deposits of ilmenite, at Piney River and the Wood property, are being mined at present, but some of the dike-like ilmenite nelsonite bodies and the disseminated rutile deposits are of present-day ore grade. Areas of intensely altered rocks near or adjacent to the border of the pegmatitic anorthosite should be investigated further so far as their containing economically recoverable titanium. / Ph. D.

Studies of Vibroseis reflection profiles over the exposed Triassic-Jurassic Culpeper, Richmond, and Scottsville Basins, and another profile over a probable early Mesozoic basin (Toano) beneath the Atlantic Coastal Plain sediments, in Virginia indicate that resolution of the geometry of the basins is inhibited by small impedance contrasts between the rock units within the basin and those bordering the basin. None of the seismic sections exhibit reflections which can be directly attributed to a Triassic-pre-Triassic interface. Resolution of the geometry of the basin sediments depends upon the presence of anomalously high or low velocity/density rock units within the basin, and similarly the presence of large amplitude reflections from within these and possibly other basins may imply the presence of these units, which include basalt and lignite. A method of analyzing the refracted waves in the seismic reflection data with large receiver offsets for determination of apparent velocities and the geometry of the refraction interface is presented. The Culpeper seismic lines indicate a basin with a maximum thickness of 2500 m along the western side and approximately 1750 m along the eastern side of the basin. The maximum thickness of the Richmond Basin below the seismic line is approximately 2700 m. The Scottsville Basin contains sedimentary strata with a thickness of 1750 m and the seismic data from the Toano Basin indicate a thickness of 3000 m. The compressional wave velocity of the strata within these basins has a range of 4000-5300 m/sec. / M.S.

Ph. D.

The Adwolf-Thomas.Bridge area of Smyth County, Virginia is underlain by Paleozoic rocks that crop out in northwest-trending belts. The formations that are considered in this study include in ascending stratigraphic order, the Erwin Formation, Shady Dolomite, Rome Formation, Elbrook Formation and Conococheague of Cambrian age and the uppermost Knox Dolomite, Tumbez Formation, Mosheim Formation, Giesler Limestone, Arline Limestone and Rich Valley Formation of Ordovician age. The area is structurally complex. The southeast dipping Seven Springs thrust brings Late Cambrian rocks of the hanging wall into contact with rocks as young as Middle Ordovician age in the Saltville thrust block. The Holston River syncline and the Glade-Pond Mountain anticlinorium form the area southeast of the Seven Springs fault. The Holston River syncline is an asymmetrical, southweat-plunging syncline in rocks of Cambrian age. The Glade-Pond Mountain anticlinorium is also confined to rocks of Cambrian age and is complicated by a series of small anticlines which have been broken on their northeast limbs by southeast dipping reverse faults. Sands and carbonates were the predominant sediments deposited in Cambrian and Early Ordovician time. In Middle Ordovician time, both carbonates and clayey muds were deposited. As no Silurian or younger Pal~ozoic sediments are present, it is not known when sedimentation ended. Deformation, perhaps in part contemporaneous with sedimentation, appears to have been' climaxed in Mississippian time after sediments of this age were deposited in the area considerably to the north of the area discussed in this report (Butts 1940). / Master of Science

M.S.

M. S.

M.S.

The geology of Roanoke and the country adjacent is conceded to be one of the most complicated structures in Virginia. On this account it has been consistently avoided in geological investigations; surveys that normally would have included Roanoke having stopped at or omitted this vicinity. It would be presumptions for the author of this paper to attempt to do what many better geologists have avoided. This paper does not attempt to give a thorough discussion of the complicated problem that the vicinity of Roanoke presents, but rather aims to condense and bring together information that has been gathered on the subject and supplement this with such additional data as could be obtained in the brief time allotted to this investigation. / M.S.

This study describes the biostratigrapaic distribution of Meramecian conodonts from three measured sections of the Greenbrier Limestone (Meramecian-Lower Chesterian), located in the Greendale and Hurricane Ridge Synclines of southwestern Virginia and southern West Virginia. The Little Valley Formation, Hillsdale Limestone and lower portions of the "Denmar-Gasper" and "Ste. Genevieve" Formations, consisting of rocks deposited in a variety of shallow carbonate-ramp environments, were investigated. Two new multielement conodont apparatuses were recognized: Kladognathus sp. A and Hindeognathus ("Apatognathus") laevipostica. Elements of Kladognathus sp. A are morphologically distinct from homologous elements of the K. levis-K. tenuis group. Evolutionary change from K. levis to K. tenuis is marked by slight Sa and Sb element changes, and the addition of an X element, DE Lambdagnathus fragilidens. Species of Kladognathus are promising Meramecian biostratigraphic markers. Also recognized in this study are species of: Cavusgqnathus, Gnathodus, Hindeodus, Idioprioniodus, Lochriea, Rhachistognathus, “Spathognathodus," Synprioniodina? and Taphrognathus. Meramecian formations in the study area can be correlated with the Mississippian stratotype (Illinois Basin) based on the following zones: Taphrognathus varians - "Apatognathus," "A." scalenus - Cavusgnathus aad Gnathodus bilineatus - Cavusgnathus charactus. Southward thickening of the "A." scalenus zone from the Hurricane Ridge Syncline (11 m) to the Greendale Syncline (180-200 m) reflects higher rates of sedimentation and subsidence in the depositional area of the latter. In addition, thinness of the zone in the Hurricane Ridge Syncline may be due to a hiatus between this zone and the younger G. bilineatus zone. This hiatus is not indicated by conodont faunas from the Greendale Syncline, which preserves a more complete Meramecian biostratigraphic record. Conodont and litahologic evidence for a coeval hiatus exists in other areas of eastern North America: the Illinois Basin stratotype, eastern Kentucky, Southern Ohio and eastern Tennessee. / Master of Science

Master of Science