CHAPTER II. 



AQUEOUS AGENCIES. 



AQUEOUS and atmospheric agencies are so closely con- 

 nected that many treat them together under the one head 

 of leveling agencies. Water, as atmospheric moisture or 

 as rain, soaking into the earth, is the chief agent of soil* 

 making ; but water, falling more abundantly, runs oil the 

 surface, and is also the chief agent of soil-removal. In 

 the one case it acts as a chemical, in the other as a me- 

 chanical, agent. The agency of water in soil-making we 

 treated under atmospheric, its agency in soil-removal be- 

 longs to aqueous, agencies. The one, acting at all times 

 and in all places, its effects are obscure and inconspicu- 

 ous ; the other, acting occasionally and concentrating its 

 power on particular places, its effects are easily observed 

 and better understood. Nevertheless, the aggregate ef- 

 fects of the one must be equal to those of the other, for 

 the former prepares the way for the latter. Aqueous 

 agencies have little effect upon rocks unless they have 

 been first rotted down to soils. 



Although the agency of water is mainly mechanical, 

 yet there is a chemical agency of water other than that 

 of soil-making. The agency of water may therefore be 

 divided into mechanical and chemical. The mechanical 

 agency is best treated under the three heads of rivers, 

 ocean, and ice, and each of these again in cutting away, 

 in carrying, and in throwing down again, or in erosion, 

 transportation, and deposit. The chemical agency we 

 shall consider under the two heads of chemical deposits 

 in springs and in lakes : 



LE CONTE, GEOL. 2 



