376 ON THE ALLUVIAL DEPOSITS. 



now is. I shall only further say, that this subject has 

 bc-en often treated by writers, and especially by De Luc, 

 in a very tedious and useless manner. 



Of Soils. 



Such is the mixed origin of the agricultural surface, 

 that it could not rigidly have been classed with any of 

 the preceding divisions. It is only where the soil is 

 untransported, that it can be dependent on the nature 

 of the rocks beneath : and such, in general, arc the 

 soils of low countries, and of lands which do not con- 

 duct rivers ; though, even in these, there is that insen- 

 sibly transported soil, which is generated by the gra- 

 dual flow of water along the surface. Were it not 

 for this, the effect of the rains would soon render bare 

 and sterile the steeper and more elevated lands : while 

 in this we must admire that provision, simple as beau- 

 tiful, by which this evil is averted ; one of those cir- 

 cles of destruction and reproduction which prevail 

 throughout nature : the same act also which removes 

 the soil, giving access to the causes which disintegrate 



the subjacent rock, 

 j 



Where a single rock is the parent of the soil, the 

 effect is easily foreseen; where more have interfered, 

 the results are proportionally complicated: while, fur- 

 ther., as already remarked, it is sometimes utterly un- 

 related to the subjacent rocks, where trap has disap- 

 peared ; as calcareous soils often also exist where the 

 parent stratum has vanished. In simpler cases, we 

 can trace the clay, the loam, the gravel, or the sand, 

 of a soil, to the original rocks ; and thus does a know- 

 ledge of these sometimes become useful to the agri- 

 culturist. He may thus even learn to foresee the 

 eventual loss of that which cannot be replaced, or, 

 from the source of eternal supply, pronounce on that 



