SOLIDIFICATION OF THE EABTH. 293 



obstinately, and with immense labour, striving to 

 build up every possible obstacle to navigation ; while 

 volcanoes, like malignant demons, destroy the exist- 

 ing basin of the ocean, or at least are incessantly 

 active in modifying its level, or filling up its hollows 

 with ashes and cinders. With our own eyes we are 

 witnesses of these and innumerable other agencies of 

 change ; and, knowing the vastness of their con- 

 sequences, we judge, in regard to past effects, what 

 causes have been in action from the results they 

 have produced. 



For this reason, the exploration of the bottom of 

 the sea is an excellent preparation to the study of 

 the past history of our planet, and of its future pos- 

 sibilities. The sea itself would not exist except for 

 the fact that the earth was originally a fiery mass, 

 the surface of which has become solidified, and 

 in the process of coohng has allowed the aqueous 

 vapours to condense. Originally extended with an 

 even surface over the whole globe, the sea served 

 everywhere as the menstruum of the first solid pre- 

 cipitations. Thenceforth the crust of the earth grew 

 in solidity and deptli, both from the exterior and the 

 interior — on the one side by sedimentation, on the 

 other by solidification. 



The cooling process continued. The crust, too 



