Industrial Minerals and Metals of Illinois

by J. E. Lamar

Marl

In some of the lakes and ponds left by the glaciers lived numerous small mollusks with calcium carbonate shells. As the animals died, their shells formed a deposit on the bottom of the lakes and ponds. Certain plants, especially algae, may have added a mudlike precipitate of calcium carbonate to the deposits, and varying amounts of clay washed from the shores mixed with both these materials. The resultant deposit is called marl. Some marl deposits have peat mixed with them, and peat also overlies some marl deposits.

Only comparatively small amounts of marl are known to have been dug in Illinois. One deposit containing many shells and shell fragments, some of it associated with peat, was worked in southeastern Livingston County as a source of agricultural liming material. Other deposits have been reported at other places in northeastern Illinois. The available information indicates that the marl deposits are likely to be principally of local importance.