Pozzolana. A kind of tuff. See [p. 36.]
Pumice. A light, spongy, fibrous form of trachyte. See [p. 373.]
Pyroxenic-porphyry, same as augitic-porphyry, pyroxene being Haüy's name for augite.
Scoriæ. Syn. volcanic cinders; reddish brown or black porous form of lava. See [p. 373.]
Serpentine. A greenish rock, in which there is much magnesia; usually contains diallage, which is nearly allied to the simple mineral called serpentine. Occurs sometimes, though rarely, in dikes, altering the contiguous strata; is indifferently a member of the trappean or hypogene series.
Syenitic-greenstone; composition, crystals or grains of felspar and hornblende. See [p. 372.]
Tephrine, synonymous with lava. Name proposed by Alex. Brongniart.
Toadstone. A local name in Derbyshire for a kind of [wacké], which see.
Trachyte. Chiefly composed of glassy felspar, with crystals of glassy felspar. See [p. 372.]
Trap tuff. See [p. 374.]