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Newest, Flcetz-Trap Formation. 199 formation, and is covered by gravel, fand, clay, wacke, &c. The kinds of coal are pitch-coal, con- choidal glance-cocil, columnar coal, common brown- coal, brown-coal including bituminous wood, earth- coal, and bituminous wood. 2. Seldom more than one bed of coal occurs in this formation, but it is ufually very thick, being from a few feet to an hundred feet thick. It occurs in great abundance in Iceland, and probably affords materials foi the fupport of the volcanoes that exift in that country ; it is found alfo at the foot of ^Etna, and probably alfo fupplies that volcano with its fuel. It occurs alfo in the ifland of Mull, and in other places in Scotland. C.—Having defcribed the different rocks that belong to this formation, we fhall now confider its more general relations, or what refpedts its ftruc- ture and relations on the great fcale. Kind of Precipitations in the Newejl Flcetz - Trap Formation. A portion of the rocks of this formation are che mical productions, another mechanical, and a third intermediate between chemical and mechanical. I he mechanical depofitions are gravel, fand, bitu minous wood, clay, and in part trap-tuff: the chemi cal are greenflone, greyflone, porphyry-ilate, pitch- ftone, compadl felfpar, obfidian, and pumice: thofe intermediate between chemical or mechanical, or what
