OF CRYSTALLISATION. 61 



the wondrous agencies which are in operation, producing 

 light-refracting gems within the secret recesses of the 

 rocky crust of our globe. 



The force of crystallisation is a subject worthy of 

 much consideration. If we examine our slate rocks, 

 through which little veins filled with quartz crystals 

 are spread, we shall see that the mechanical force 

 exerted during the production of these crystals has 

 been capable of rending those rocks in every direc- 

 tion. Those fissures formed by the first sy tsem of crystal- 

 line veins, in order of time, are filled in by another set 

 of crystalline bodies, which equally exert their mechani- 

 cal power, and thus produce those curious intersections 

 and dislocations which were long a puzzle to the geo- 

 logist. The simplest power, slowly and constantly 

 acting through a long period of time, may become 

 sufficient, eventually, to rend the Andes from base to 

 summit, or to lift a new continent above the waters of 

 the ocean. 



