Abstract KENTUCKY marls or calcareous clays are usually soft, calcareous-magnesian shales or soft, clay-containing magnesian limestone which breaks down on weathering into finely divided particles. In recent years marl has been used extensively because of its cheapness and easy accessibility, as a source of lime for soils. The neutralizing values of these marls vary from 20 to 98 percent (estimated as calcium carbonate). Because of the general distribution of marls in certain localities in Kentucky the establishment of their value as sources of calcium for laying hens is of economic interest. Three typical marls and a high grade limestone were selected, the analyses of which were: These marls and limestone were ground to pass through a 100-mesh sieve and added to a basal ration which consisted of shipstuff 60, ground yellow corn 20, meat scrap 20 and cod liver oil 1 pound and fed to Rhode Island Red pullets. The analysis . . .