542 THE UNIVERSE. 



do not find among them any trace of organized beings, but, 

 by way of compensation, they contain the principal riches 

 which Nature elaborates in the splendid laboratories of her 

 alchemy. 



Metalliferous layers often lie in veins, huge cracks in the 

 globe filled with divers materials. Philosophers guided only 

 by the power of intuition Descartes and Leibnitz had 

 taken up perfectly correct ideas as to the theory of their 

 formation. They considered that the ores and other sub- 

 stances met with in the rocks had filled up the clefts by 

 solidifying there, having escaped in a state of vapor from 

 the burning beds below. Werner demonstrated this in a 

 very plausible way, and modern geologists have accepted 

 his views, at the same time modifying them a little. 



In his beautiful work " La Vie Souterraine," M. Simonin 

 maintains that these metallic emanations may reach the fis- 

 sures in two ways. " They are deposited in the fissures 

 which constitute the veins either in the state of vapor by a 

 dry method, as in the craters of volcanoes or the chimneys 

 of smelting furnaces ; or in a state of chemical precipita- 

 tion by a wet method, as in the solutions of our labora- 

 tories." 



This hypothesis, as the author tells us, meets all objec- 

 tions, explaining at the same time the deposit and the for- 

 mation of the matrix which envelops it. 



Granite and porphyry must be classed among the richest 

 metalliferous rocks, but beds of ore are also met with in the 

 old transition rocks. It is in these that gold and silver are 

 found. The placers of California are often formed merely 

 by the detritus of granite rocks and schists filled with par- 



