28 MEMOIR OF 



quired the most intimate acquaintance with these 

 laws, and could read in them the history of all the 

 revolutions from which they had resulted. Follow- 

 ing each bed in the order of its continuity, without 

 allowing himself to he bewildered by rents and shift- 

 ings, or by the crests and other summits which rise 

 above them, he in some measure determined their 

 age, and the age of all the accessory matters which 

 intermingle with their principal substances. 



The different fluids which have surrounded the 

 globe, the changes in composition which they have 

 undergone, and the violent commotions by which 

 each change has been accompanied, were all legible 

 to his eyes on the monuments which they have left 

 behind them. 



A universal and tranquil ocean deposites in large 

 masses the primitive" rocks, which are strongly crys- 

 taJlized, and have silica for their predominating in- 

 gredient. Granite forms the base of the whole. To 

 this succeeds gneiss, which is nothing more than 

 granite beginning to assume a slaty structure. By 

 degrees, argil begins to predominate. Schists of 

 different kinds appear ; but in proportion as the pu- 

 rity of the precipitations becomes changed, the dis- 

 tinctness of the crystalline grain diminishes. Ser- 

 pentines, porphyries, and traps succeed, in which 

 the grain is less distinctly formed, although a sili- 

 ceous nature begins to resume its purity. Internal 

 agitation in the fluid destroys a portion of these pri- 

 mary deposites ; and their debris forms new rocks. 



