542 MANUAL OF NATURAL HISTORY. 



I. CLASS.— HYPOGENE-FORMATIONS. 



This class, comprising the Granitic and Trap 

 Rocks, the Gneiss, and Mica-Schist, is composed of 

 hard, compact, crystalline strata, and solid rocks of 

 quartz and mica. Granite, syenite, hornblende, 

 serpentine, together with basalt, chink-stone, and 

 clay-stone, also occur, and organic remains are 

 absent. 



I. — The Granite-Basis. 



The unstratified and crystalline granite basis, on 

 which all the other formations rest, is generally 

 believed to have resulted from the gradual cooling 

 of the earth when liquified by intense heat. The 

 crust of solid granite thus formed, is estimated at 

 sixty to one-hundred miles thick, and it is imagined 

 that it will continue to increase in thickness as the 

 process of cooling goes on. This granite crust is 

 flexible, and the expansive force which the fluid 

 nucleus exercises upon it, is believed to occasion the 

 phenomena of earthquakes. Portions of it are 

 found protruding above the other strata in every 

 part of the globe, often rising up in extensive 

 mountain-chains, as in the Andes of South America, 

 the Abyssinian ranges of Africa, the Pyrenees of 

 Spain, the Grampians of Scotland, the Alps of 

 Switzerland, and the Cornwall hills of England. 



1. — Common Granite is composed of felspar, 

 quartz, and mica ; when hornblende is present 

 instead of mica, it is Syenite ; when talc takes the 

 place of mica, it becomes Protogine; when it is 



