v.] SOILS AND SUBSOILS 97 



subsoil are very much alike, the soil being generally a 

 little the poorer, because of the constant solution that 

 is going on in the surface soil. On the other hand, the 

 surface soil has sometimes been so regularly dressed 

 with chalk or lime that it shows a higher percentage 

 of carbonate of lime than the subsoil. Soils on chalk 

 or limestone formations are often very shallow, so that 

 the subsoil becomes nearly pure carbonate of lime, 

 wherever a subsoil can be said to exist. As regards 

 sands and clay, in the heavier soils — i.e., the true clays, 

 the heavy clay loams, and most alluvial soils — the surface 

 soil is more coarsely grained than the subsoil ; it contains 

 more sand and less clay. This difference is due to the 

 constant action of the rain washing down the finest 

 particles, especially when the soil is loose after cultiva- 

 tion. When the rain beats upon the rough surface of 

 the soil, some of the very finest particles become washed 

 off and suspended in the water ; sometimes they are 

 filtered out again by the soil at a lower level, sometimes 

 they are carried away into the ditches ; in either case 

 the coarser-grained material is left behind on the top. 

 The subsoil, however, of a sandy soil possesses much the 

 same composition as the soil ; in this case there is both 

 less fine material to wash down, and also the whole soil 

 settles together when beating rain falls, instead of leav- 

 ing the hollow spaces which occur in a clay soil for a long 

 time after it has been worked. As to the comparisons 

 between different kinds of soils, we find that all the 

 heavy working soils (really the lightest per cubic foot) 

 are made up of the finer particles, and contain but little 

 sand ; especially do they contain very little of the coarsest 

 sand, which tends to keep a soil open and friable: They 

 are distinguished by a high proportion of clay, though 

 of what the analyst properly calls clay — material made 

 up of particles less than one hundred and twenty- five 



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