ABSENCE OE MOUNTAINS 8 



J 



amounts of dust thrown out of volcanoes as well as that 

 which falls from the celestial spaces. In a word, the land is 

 characteristically the place where the strata are in the course 

 of destruction, and the sea-fioor the laboratory where these 

 materials are separated from the water, partly by gravity and 

 partly by the growth of organic forms, and built again into 

 compact rocks. 



The result of these differences in conditions is, that while 

 the land is carved into innumerable vallexs which mark the 

 process of its destruction, the sea-floor is approximately 

 level, for that is the shape which the growing deposits 

 assume as they are accumulated. But there are yet other 

 influences which serve to give to the sea-floor a uniform 

 aspect. Chief among these we must reckon the prevailing 

 absence of true mountains in the fields which are covered 

 by the ocean waters. Although these vast realms contain 

 numerous elevations, some of which are of magnificent pro- 

 portions, it seems tolerably certain that true mountains — that 

 is, elongated heights produced by the folding of rocks into 

 rido-es and furrows — do not occur in the abysmal portions 

 of the ocean. 



The evidence of this lack of mountains in the deep seas, 

 though inferential, is very satisfactory in its nature. We 

 note that the average depth of the oceans, as determined by 

 many thousand soundings as well as by the speed with which 

 the waves caused by earthquakes travel over their basins, is 

 about fifteen thousand feet, while the portion of the marine 

 fields where the depth exceeds twenty thousand feet is 

 extremely limited, and the most profound abyss yet encoun- 

 tered in sounding is only about twenty-eight thousand feet 

 below the surface. In the land we find many hundred peaks 



