TUFF

rock débris consisting of volcanic ashes and igneous rocks of fine-grained material; varieties: Tracontains orthoclase, biotite, augite, and hornblende; Sasaltiuff, composed of basalt and found in Skye, and Mull; Pumice-iuf, gla y fragments and pumiceous matter; Rhyolite tuff, composed chiefly of rhyolite.