112 THE FITNESS OF THE ENVIRONMENT 



Relatively few of these bodies are highly 

 insoluble; very many are exceedingly soluble 

 in water. Apart from their electrolytic dis- 

 sociation and hydrolysis, which will be later 

 discussed, the chemical changes wrought upon 

 such dissolved substances in solution are 

 commonly very unimportant. For chemical 

 inertness, depending upon great stability, 

 is a most significant characteristic of water, 

 and undoubtedly a highly advantageous one 

 as well. 



On the whole the best evidence for the 

 efficiency of water as a solvent of inorganic sub- 

 stances is to be found in the data of geology. 

 Of all geological agents water appears to 

 have been by far the most active within the 

 periods of which investigation is made pos- 

 sible by the geological record. 1 Rainfall, 

 the movement of surface streams and of 

 water beneath the ground, and wave action, 

 all contribute to the work of disintegration, 

 sedimentation, etc., partly by dissolution of 

 soluble material, partly by mechanical action. 

 But mechanical action is itself much in- 

 creased by the loosening which earlier dis- 

 solution has caused. In this manner the great 

 solvent power of water throughout its meteor- 

 ological cycle largely contributes to the mobil- 



1 Geikie, "Textbook of Geology," pp. 447-597. 



