THE FOUNDATIONS OF THE CONTINENTS 8l 



would perhaps force out and cause to flow over the 

 surface beds of molten material from below the 

 crust, and differing somewhat from it in their com- 

 position. All this aqueous work would accelerate 

 the cooling and thickening of the crust, and at 

 length a universal or almost universal heated 

 ocean would envelope the globe, and so far as its 

 surface was concerned, the reign of water would 

 replace that of fire. We may pause here to con- 

 sider the probable nature of the earth's crust in 

 this condition. 



The substance most likely to predominate would 

 be silica or quartz, one of the lighter and most 

 infusible materials of the crust ; but which, heated 

 in contact with alumina, lime, potash, and other 

 earths and alkalis, forms fusible slags, enamels and 

 glasses. One of these, composed of silica, alumina, 

 and potash, or soda, was long ago named by the 

 German miners felspar, a name which it still retains, 

 though now several distinct kinds of it are dis- 

 tinguished by different names. Another is a 

 compound of silica with magnesia and lime, form- 

 ing the mineral known as Amphibole or Horn- 

 blende, and by several other names, according to 

 its colour and crystalline form. In many deep- 



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