222 GEOLOGY AND CHEMISTRY OF SOILS. 



The soil A, which has never been cultivated and which 

 was the most fertile, has the greatest quantity of crenic and 

 humic acids, but the soil B, which has bfeen exhausted, con- 

 tains less than 1 per cent., although it contains a greater 

 quantity of apocrenic acid than either. This acid, however, 

 and its salts are supposed to exert but little influence in vege- 

 tation. C, the sub-soil of B, appears to have received nu- 

 tritious matter from the soil, and would doubtless yield a lar- 

 ger crop than the soil itself. Here, then, we have developed 

 two important facts: 1. That the fertility of a soil depends 

 upon the humic and crenic acids. 2. That fields long culti- 

 vated and almost exhausted, may be rendered fertile by sub- 

 soil ploughing. 



It may be further seen, that lime, a substance essential to 

 fertility, is most abundant in the sub-soil, having been carried 

 down from the soil in combination with humic and crenic 

 acids. This is another mode by which the soil becomes de- 

 prived of lime and alkali. 



The second example we will instance, is that of three soils 

 from Rhode Island, analyzed by Dr. C. T. Jackson. 



The three specimens were originally of the same character. 



A, soil in its natural state, that would not produce more than 

 10 bushels of corn to the acre, less of other grain, and no hay. 



B, has been improved by ashing only, and produces I J tons 

 of clover. C, is in a high state of cultivation, and has pro- 

 duced, in a three years' rotation, 60 bushels of corn, 50 of 

 oats, and two tons of hay per acre. 



The coarser pebbles and vegetable fibres were all taken out 

 by sifting the soil through a fine sieve, and 100 parts of the 

 fine materials were subjected to analysis. 



A. 



Water of absorption 1 .80 



Soluble vegetable matter 2.50 



Insoluble vegetable matter 2.00 



Peroxide of iron 2.10 



Alumina 2.10 



