Marl, an earthy rock containing lime mixed with clay or sand or both. One of the commonest forms of it is the shell-marl of fresh-water lakes, which consists of the remains of mollusks, entomostracans, and algse, and is generally white. It accumulates in lakes, where there is little mechanical sediment, or if any then in times of flood, producing interlamination of marl and clays. Such deposits occur under the peat on the sites of former shallow lakes in Ireland and Scotland. Fresh-water limestones and clays of similar origin occur on a larger scale in the Eocene rocks of Wyoming, and in the Miocene of Switzerland and Auvergne. The shell sand of the Crag is practically a marine marl. As marl is a very valuable substance to add to stiff clay land, both because it lightens the soil and because it furnishes it with lime, the term marling is sometimes extended by farmers to the addition of merely sandy soil, and such loam (q.v.) is miscalled marl.