BIRLIOGRAPIIY. Orton. The Andes and the Amazon (New York, 1870) ; Crawford, Across the Pampas and Andes (London, 1334) ; CUssfeblt, Heise in den Asides (Berlin, 1838) ; Whym per, Travels Among the Grrat Andes of the Equa tor (London, 1892) ; Fitzgerald, The Highest Andes (New York, 1899) ; Conway, The Boliv ian Andes (New York, 1901) : Reclus, Physical Geography, translated and edited by Keane and Ravenstein (London, A volcanic effusive rock of por phyritie texture composed essentially of lime soda feldspar (andesine) with black mica (bio tite), hornblende, or augite imbedded in a ground mass of smaller crystals or rock glass. The structure may be, but is not necessarily, porous; in most eases the crystals of andesine are ar ranged roughly parallel, giving the rock its char acteristic fluxion or andesitie structure. This structure is due to the flow of the once molten mass in the form of lava. In composition this
family of rocks shows wide variations, limited, however, by the rhyolites (9.v.) and trnehytes (q.v.) on the one hand, and the basalts on the other. Fairly rich in silica and alumina, they contain moderate amounts only of the heavier and darker bases, viz., iron, lime, and magnesia. The) contain from 60 to 70 per cent. of silica, 13 to IS per cent. of alumina, 4 to 9 per cent. of iron. 3 to 6 per cent. of lime, 5 to 9 per cent, of alkalies, and smaller percentages of magnesia. They owe their name to their extensive develop ment in the Andes of South America, though they occur extensively throughout the entire Cor dillera]) system of mountains, in South, Central, and North America. See RHYOUTE; TRAOHYTE.