INTEODUCTOEY 3 



ment. Tlie summer's heat and winter's cold, the chemical action 

 of atmospheres and acidulated rains, combine their forces; a 

 breaking up ensues, to be succeeded by new combinations and 

 perhaps reconsolidations more in keeping with existing circum- 

 stances. An intermediate product in all this endless cycle 

 of change, of disintegration and recombination, is a compara- 

 tively thin, superficial mantle of loose debris, which, mixed with 

 more or less organic matter, nearly everywhere covers the land, 

 and by its combined chemical and mechanical properties fur- 

 nishes food and foothold for myriads of plants, and hence, 

 indirectly, sustenance for man and beast. In brief, what is 

 commonly known as soil is but disintegrated and more or less 

 decomposed rock material, intermingled, perhaps, with organic 

 matter from plant decay. Such being the case, a study of the 

 processes of rock weathering and the transportation, deposition, 

 and physical properties of the resultant debris, is but a study 

 of the origin of soils on the broadest and most comprehensive 

 basis. Their study belongs as legitimately to the realm of 

 geology as does that of any subject relating to rock formation 

 or other phases of the earth's history. 



Accepting the above, the various phases of the subject will be 

 taken up in the following order: (1) the elements which in their 

 single or combined state make up the minerals ; (2) the minerals 

 which make up the rocks; (3) the rocks themselves, with par- 

 ticular reference to their mineralogical and chemical natures; 

 (4) the breaking down or degeneration of rocks through proc- 

 esses in part chemical and in part mechanical; and (5) the 

 result of this clasmatic process as manifested in the production 

 of clay, sand, gravel, and incidental soil. There are other points 

 which will be touched upon more briefly, in order to make the 

 work systematic, as the action of wind and water in assorting 

 and redepositing rock debris and tending to reduce the land 

 surface to one general level. 



