pumice
peat
mulch
humus
leaf mold
clod
loam: a rich, friable soil containing a relatively equal mixture of sand and silt and a somewhat smaller proportion of clay.

marl:  Geology. a friable earthy deposit consisting of clay and calcium carbonate, used especially as a fertilizer for soils deficient in lime.

argil: clay, especially potter's clay.

bole:
noun
1.
any of a variety of soft, unctuous clays of various colors, used as pigments.
2.
a medium red-brown color made from such clay.





clutch
kaolin
loess: a loamy deposit formed by wind, usually yellowish and calcareous, common in the Mississippi Valley and in Europe and Asia.
slip
till: a stiff clay, a glacial drift of clay, sand, gravel, and boulders