74 THE FITNESS OF THE ENVIRONMENT 



that the incomparable mobility of water, 

 which depends upon its peculiar physical prop- 

 erties and upon its existence in vast quanti- 

 ties in all three states of solid, liquid, and 

 gas, is the chief factor among the properties of 

 matter to determine the nature of the phenom- 



upon the presence of the atmosphere, upon the relief of the 

 land, and upon the radiant energy of the sun. Through the 

 agency of rainfall, of surface streams, of underground waters, 

 and of wave action, the hydrosphere is constantly modifying 

 the surface of the lithosphere, while at the same time it is 

 bearing into the various basins the wash of the land and 

 depositing it in stratified beds. It thereby becomes the 

 great agency for the degradation of the land and the building 

 up of the basin bottoms. It works upon the land partly by 

 dissolving soluble portions of the rock substance, and partly 

 by mechanical action. The solution of the soluble part usu- 

 ally loosens the insoluble, and renders it an easy prey of the 

 surface waters. These transport the loosened material to 

 the valleys and at length to the great basins, meanwhile roll- 

 ing and grinding it and thus reducing it to rounder forms and a 

 finer state, until at length it reaches the still waters or the low 

 gradients of the basins and comes to rest. The hydrosphere 

 is, therefore, both destructive and constructive in its action. 

 As the beds of sediment which it lays down follow one another 

 in orderly succession, each later one lying above each earlier 

 one, they form a time record. And as relics of the life of 

 each age become more or less imbedded in these sediments, 

 they furnish the means of following the history of life from 

 age to age. The historical record of geology is, therefore, very 

 largely dependent upon the fact that the waters have thus 

 buried in systematic order the successive life of the ages." 

 — Chamberlin and Salisbury, "Geology." New York, 

 1904, Vol. I, p. 8. 



