The geology of the upper Roanoke River Valley area, Montgomery and Roanoke counties, Virginia

Abstract

The upper Roanoke River Valley area lies in the Valley of Virginia in Montgomery and Roanoke counties, and is about 100 square miles in area. All but the oldest of the mapped units shown on Plate l are of Paleozoic age and of sedimentary origin. The Precambrian rocks that crop out on Poor Mountain were not subdivided or studied in detail in the field. The aggregate thickness of the Paleozoic rocks in the area is approximately 5,600 feet. However, parts of these formations are either cut off by faults or are covered by overthrust sheets.

The structure of the area consists of two overthrust sheets and several small anticlinal folds in formations of the overridden block. The lower overthrust sheet (Salem thrust block) has considerable stratigraphic displacement; a formation of Middle Cambrian age has been brought into contact with formations which range in age from Cambrian to Devonian. The upper overthrust sheet (Max Meadows thrust block) has only slight stratigraphic displacement, as the formations on either side of the fault are of Cambrian age. An extensive zone of breccia is associated with the fault beneath the upper overthrust sheet. Minor faults and folds are present in the formations of both overthrust sheets as the result of deformation both prior to and during movement along the faults.

The only operations at the present time which utilize the mineral deposits of the area are quarries in shales to supply a brick plant. Limestone and dolomite for crushed stone have been quarried in the past. Traces of lead and zinc sulphides and iron are also present.

Ground water in quantities of economic importance may be present within solution channels in dolomites of the Rome and Elbrook formations. In general, the alluvial deposits in the area are too thin and contain too much interstitial clay to be of importance as large sources of ground water.