Limestone rocks are an important source of ground water in the Piedmont and Appalachian areas of Maryland. The major limestone aquifers are the Cockeysville and Wakefield marbles and the Silver Run, Tomstown, Frederick, Grove, Waynesboro, Elbrook, Conococheague, Beekmantown, Stones River, Tonoloway, Helderberg and Greenbrier formations. Drilled and dug wells and springs are common sources of water supply in the limestone areas. The depths of 298 limestone wells range from 8.7 to 1,800 feet and average about 150 feet. The yields of these wells range from 0.1 to 575 gpm. Specific capacities, or yield per foot of drawdown, range in 137 wells from < 0.1 to 43 gpm per foot. Springs are common in the limestone areas and their flow varies widely at different times. Most of the known springs are of the 5th magnitude or lower, and therefore have a mean flow of less than 100 gpm. The quality of water from the limestone aquifers is satisfactory for most purposes, but is commonly hard and slightly alkaline. The limestone aquifers are large essentially untapped ground-water reservoirs whose hydrologic character is only partially understood.