CHEMISTRY OF THE ROCKS. 55 



in fusion would evaporate others. Some therefore must have 

 been contained in the atmosphere as simple gaseous elements. 

 Inasmuch as granite is beneath all the other formations, if we 

 show that this must originally have been in a gaseous state, we 

 show that every other material must have been at the same time 

 in like condition. 



The granite rocks are by far the most abundant terrestrial sub- 

 stance that we know of. Geologists assign to them a depth of 

 not less than thirty miles. And still below them there is the 

 same or nearly the same chemical substance in fusion, as the fact 

 and analysis of volcanic products sufficiently prove. The com- 

 pound which is in excess in all granite rocks is silica, the oxide of 

 the element silicon. The varieties are formed chiefly by small 

 percentages more or less of the oxides, alumina and magnesia. 

 This silica, or quartz, as well as the other components of the 

 igneous rocks, is what has been termed "burnt material." It is 

 the product of a most complete and tremendous conflagration ; 

 for the oxidation of silicon is as much and as powerful a com- 

 bustion as the oxidation or burning of coal. To accomplish this 

 burning, every particle of the silicon must have been brought 

 into contact with oxygen gas. This would have been simply im- 

 possible if the mineral element had always been in a melted mass 

 of miles in depth ; for this, if for no other reason, that the oxy- 

 gen could never have got at it certainly not, if it was covered 

 by other solid or liquid substances. -Or, if it were conceded that 

 silicon ever formed the surface of the earth, then all other 

 materials of what is now the crust must have been gases above 

 it ; arid as nine-tenths of the elements in vapor are heavier than 

 oxygen many of them more than ten times as heavy this gas 

 could never have even touched this imaginary sea of silicon. 

 The oxidation then was only possible in the regions of the 

 atmosphere, where oxygen existed and abounded. There only, 

 among the free-moving gases, could the incalculable amount of 

 heat evolved in the combination be carried off. 



We confidently assume therefore that the whole of this most 

 abundant mineral element once existed in the atmosphere in the 

 form of a high-heated gas ; and that some time and somewhere, 



