THE AGE OF SOILS 377 



handed down from the strata earlier decomposed. In such a case 

 as that figured on p. 291, we have a residual soil containing the 

 least soluble constituents of the hundreds of feet of dissolved 

 and disintegrated rock which once extended across the entire 

 country, becoming commingled with that now undergoing, in 



FoofrSovb 



Fig- 39. 



its turn, the soil-making process. Such a soil may, therefore, 

 in extreme cases, contain materials of all ages from the first 

 product of disintegration of the uppermost strata, which may 

 have been Carboniferous, to that which formed to-day, and may 

 be Cambrian. 



It is, of course, true that through the erosive action of water 

 these soils are continually losing their finer silt and clay-like 

 particles, it may be almost as fast as formed, especially in hilly 

 regions, and that as the soil drops lower and lower in the geo- 

 logical horizons indicated, it becomes more and more impover- 

 ished in those constituents derived from the upper beds. But 

 as to what proportion of the material of one horizon is handed 

 down to become admixed with that from the rocks below, we 

 have no means of judging, and in fact it must be ever-varying. 



The matter of the geological age of any soil, or the age of 

 the rocks from which it was derived, is therefore of only very 

 general interest, and may well be dismissed here. The attempt 

 which has been made by another writer^ to discriminate or 

 classify soils according to the geological horizons of the rocks 

 from which they were derived, is believed by the present writer 

 to be futile and wholly inexpedient 



No attempt should be made, as has been done by at least one 

 writer, to state the character of soil that may arise from the 

 weathering of any particular class of rocks, since much depends 



=^See Stockbridge 's Eocks and Soils, p. 12. 



