The area described in this report includes the northern and central parts of Shenandoah Valley in Virginia extending from the West Virginia line southwestward to the vicinity of Greenville, Augusta County. It contains extensive deposits of high-calcium limestone averaging more than 97 per cent calcium carbonate. The Mosheim limestone, composed largely of high-calcium limestone, is the important "quarry rock" of the area. Other formations containing high-calcium limestone include locally a part of the Lenoir, the upper part of the Chambersburg in the western belts of Shenandoah County, and relatively thin units in the Beekmantown along the eastern side of the Massanutten Mountain syncline north of Rockingham County. Some of the thickest deposits of high-calcium limestone near railroads are in Frederick, Shenandoah, Rockingham, and Augusta counties.
Extensive exposures of the Tomstown (Shady) dolomite, containing more than 42 per cent magnesium carbonate, occur in the eastern part df Clarke County. Locally near the North Mountain fault in parts of Shenandoah and Rockingham counties, 80 feet or more of brecciated dolomite in the Elbrook formation contains about 43.5 per cent magnesium
carbonate and generally less than 2 per cent silica. Most of the sampled dolomite units in the Elbrook, Conococheague, and Beekmantown formations contain less than 40 per cent magnesium carbonate.
Special study was made of the carbonate rocks suitable for chemical use and favorably located near railroads. Limestones, containing less than 95 per cent calcium carbonate, were studied locally in some detail. Descriptions of the belts of industrial limestone and dolomite are supplemented by geologic maps and sections, and chemical analyses.
