ORIGIN OF SOILS. 17 



modified resemblance, the knowledge of which will be 

 of service when dealing, in the first instance, with 

 large pending operations. 



The origin of soils has been so often written about, 

 that it seems unnecessary to reproduce the subject 

 here ; we may, however, remind the reader that soils, 

 so called, are the disintegrated surfaces of the under- 

 lying formations, not necessarily partaking of the 

 exact character and ingredients of that immediately 

 underlying or adjacent ; because most of our deep 

 soils are the drifts from the detritus of the denuded 

 or exposed surfaces of the stratified rocks, which have 

 been collected and arrested from time to time by 

 natural agencies, thus filling up the crevices caused 

 by the unequal and diversified surface of the crust 

 below. For an example we may turn to the soils of 

 the chalk formation, where we find a great variety, 

 and of various depths. These soils are mainly com- 

 posed of the plastic clay and sand of the tertiary 

 formations which have filled up the pits and fissures 

 of its surface. 



It must be clear that if every exposed surface of 

 stratified rock, by its disintegration, yielded a univer- 

 sally similar soil, as it would do if not exposed to 

 further action, we should have, in place of the diver- 

 sified soils, soils of fixed type and character, often of 

 little or no value. It is the blending of the various 

 ingredients which give the value to the surface soils, 

 and which we take advantage of in all our acts of 

 culture. 



This natural blending, attended by the accumula- 

 tion of the residue of organic substances, yields fertile 



B 



