argil                   clay. (and |argillaceous|, etc.)
gyttja                  (geol.) an organic-rich mud found on the floor
                        of certain lakes.
tephra                  ash, cinder, and other fragmented volcanic ejecta.
malm                    a soft limestone; a chalky soil of SE England;
                        a mixture of chalk and clay for making bricks.
gangue                  the earthy matrix in which a vein of ore is embedded.
bole                    a red-brown color; soft clay used as a pigment.
drumlin                 (geol.) a hill of glacial drift.
stade                   the period of time represented by a glacial deposit.
edaphon                 the fauna of the soil.