v.] SOILS AND SUBSOILS 95 



a thousand tons. If, then, a soil possesses as little as 

 one-tenth per cent of nitrogen, it still contains about a 

 ton of nitrogen per acre down to the depth of 9 inches 

 only ; yet, as we have seen earlier (Table VI.), an 

 ordinary crop does not remove from the soil more than 

 50 to 100 lb. of nitrogen per acre. There is thus material 

 for fifty or more full crops in the poorest soils; but 

 these questions will be discussed more in detail in a 

 later chapter. 



We may now return to the rough soil analyses we 

 have made, to see what light they throw on the relative 

 nature of the soils and subsoils. For purposes of 

 illustration, Table XII. (page 96) gives more accurate 

 and detailed analyses of such a series, in which the 

 soils have been split up into a larger number of frac- 

 tions than was attempted in our rough analysis ; each of 

 the fractions in the first case included two of the frac- 

 tions into which the soil is separated in the full analysis. 



Looking down this table we first notice that there is 

 comparatively little humus in the subsoils ; the humus is 

 almost wholly confined to the 9 inches in which the 

 roots are numerous. Exceptions to this rule are 

 furnished by the alluvial and sometimes by the peaty 

 soils if the soil has been taken from the top of a peat 

 deposit of any depth, because peat is nothing more than 

 an accumulation of former vegetation in a more or less 

 pure state. The alluvial subsoils always show a con- 

 siderable amount of humus, because down to their 

 lowest depths they consist of old soil which has been 

 washed off the surface into the rivers in flood time, and 

 redeposited lower down the river. Only when the 

 alluvial subsoil consists of coarse-grained gravel or sand 

 will it be poor in humus ; these large particles naturally 

 carry no humus after rubbing together for a time in 

 running water. As regards carbonate of lime, soil and 



