boulder clay(n = noun.substance) till - unstratified soil deposited by a glacier; consists of sand and clay and gravel and boulders mixed together;
is a kind of dirt, soil

bleaching clay, boulder, boulder fern, cassius clay, cassius marcellus clay, china clay, clay, clay pigeon, clay pipe, clay sculpture, glacial boulder, henry clay, henry clay frick, indurated clay, lucius clay, lucius dubignon clay, pipe clay, porcelain clay, potter's clay, red clay, residual clay, river boulder, sedimentary clay, shore boulder