AGE OF MOLLUSKS. 187 



or sunk in the west beneath the undefined and murky 

 horizon." So great was the heat that prevailed while 

 the azoic strata were laid down that it does not seem 

 strange that no remains of life are found in them. "As 

 well," says Agassiz, " might we expect to find the re- 

 mains offish, or shells, or crabs at the bottom of geysers 

 or of boiling springs, as on those early shores, bathed by 

 an ocean of which the heat must have been so intense." 

 272. State of the Surface at the End of this Age. At 

 the end of the Azoic age there was nothing like the di- 

 versity of surface that there is at the present time, there 

 being no high elevations over the comparatively small 

 portions of land which then rose above the level of the 

 universal ocean. Still, denudation had been going on 

 during all the progress of the age, and there were there- 

 fore extensive areas where there were gravel, sand, and 

 some material ground up so fine as to be mud. This 

 broken and ground material was spread not only here 

 and there over the land, but over the bottom of the seas 

 as now. In short, the earth was prepared for the com- 

 ing life of the next age. A part of this preparation was 

 the reduction of the temperature to such a point as was 

 consistent with the existence of plants and animals. 



CHAPTER XIV. 



AGE OF MOLLUSKS, OR SILURIAN AGE. 



273. Dawn of Life. The earth having been prepared 

 during the Azoic age for vegetation, life, both vegetable 

 and animal, was now introduced upon the scene. That 

 its introduction occurred at that time is inferred from 

 the fact that the beginning of the life-record is found in 

 the rocks that were then formed, or, in other words, that 

 no fossils, no remains of life, have been found in the 

 rocks that were formed previous to that period. There 



