PART V. 



AGRICULTURE 



CHAPTER I. 



FORMATION AND ELEMENTS OF SOILS. 



THE soil is composed of disintegrated rocks, animal and 

 vegetable matters : most soils are made up of successive layers 

 of fine sand and organic matters, loam, fine gravel, clay, coarse 

 gravel, and occasional masses of rock of various sizes. Various 

 causes have concurred to produce the alluvial deposit on the 

 surface of the earth, which must ultimately have been formed 

 entirely of the rocks which constitute the solid basis and prin- 

 cipal bulk of the globe. 



The running water of rivers and the great ocean current 

 which sweeps across the earth had denuded the rocks which 

 it washed in its course from the high Lpds to the plains and 

 valleys : in this way, ravines have been excavated, valleys filled 

 up, and vast level plains formed. The floods formed by rains, 

 and the torrents resulting from melted snow and ice, which 

 flow down the mountains' sides, wash away all loose matters, 

 and often undermine and tear away fragments of rock : these 



