io The Founders of Geology LECT. 



allowed the pent-up waters to rush out. Buffon's theory 

 was hardly less fanciful. But he reversed the order of 

 events. He inferred from the abundance of fossil shells 

 that there had once been a universal ocean, and that by 

 . the giving way of the crust, a portion of the waters was 

 engulfed into caverns in the interior, so as to expose what 

 are now mountains and dry land. 



For some thirty years after the publication of his 

 Theory, Buffon continued to work industriously in all 

 departments of natural history. At last, in 1778, he re- 

 turned to the question of the origin of the earth and pub- 

 lished his Epochs of Nature. In this work he arranged 

 the history of the globe in six epochs intervals of time 

 of which the limits, though indeterminate, seemed to him 

 none the less real. The first epoch embraced the primeval 

 time when the earth, newly torn from the sun, existed still 

 as a molten mass which, under the influence of rotation, 

 assumed its oblate spheroidal form. The transition from 

 fluidity to solidity, and from luminosity to opacity was 

 brought about entirely by cooling, which commenced at 

 the outer surface. A crust was thus formed, outside of 

 which the substances, such as air and water, which were 

 not solidified by the lowering of temperature, remained as 

 a fluid or aeriform envelope, while the interior still con- 

 tinued for a long time liquid. 



Buffon's second epoch was characterized by the con- 

 solidation of the molten globe, and the appearance of 

 hollows and ridges, gaps and swellings, over its surface. 

 These inequalities in the crust of granite, gneiss and other 

 ancient crystalline rocks, gave rise to the mountains and 

 valleys of the higher portions of the land. 



