8 



Causes and Course of Organic Evolution 



recognize that these elevations and depressions were funda- 

 mentally different in distribution, situation, and connection 

 from those of the present day, or even of the mesozoic period. 

 Gradually, therefore, through intimate union of the cooling 

 materials of the crust, there formed upon the igneous rock 

 masses that extremely complex layer of fundamental solid 

 rock that we know as granite. From all geological evidence, 

 this is the primitive crystalline zone on which all the more 

 recent strata have been deposited, and even from which in 

 great part they have been derived, by subsequent decomposi- 

 tions and denudations. It may therefore be of value here to 

 give a tabular view of the composition of granite in nine of 

 its most abundant components, that together make up about 

 99.75 per cent, of its composition. 



From the above table it will be seen that the most striking 

 peculiarities of granite are: (1) the presence in it of all the 

 elements needed for complete nutrition of plants and animals 

 except those three fundamentally diverse elements already 

 referred to, carbon, hydrogen, and nitrogen. But undoubtedly 

 the three existed in abundance in the surrounding gaseous 

 envelope that constituted the atmosphere of the evolving earth. 

 For CO2 has all along played an important part in uniting 

 with bases to form carbonates, while the masses of grapliite 

 that occur in the older crystalline rocks prove that it must 

 have been abundant. Nitrogen must also have been a widely 

 diffused gas in the atmosphere, but its presence otherwise is 

 demonstrated by its frequent occurrence in cavities of granite, 

 gneissose and basaltic rocks. The same is true for hydrogen. 



