230 



GEOLOGY AND CHEMISTRY OF SOILS. 



produce bountifully, if their own stores are not well sup- 

 plied with all the necessaries and comforts of life. 



Sect. 5. Classification and Description of Soils. 



As all soils originate from the decomposition and disinte- 

 gration of rocks, effected by the chemical >and mechanical 

 agency of air, water, and vegetation, to which small quanti- 

 ties of vegetable and animal matters are added, the most ob- 

 vious mode of classification would seem to be that derived 

 from the geological character of the rocks. For we should 

 expect that soils would resemble the rocks from which they 

 originated, and (with the exception of some cases of great dis- 

 turbance by glacial action, or running water, in which cases 

 several varieties of rock are mingled together), that the rock 

 from which the soil originated would underlay it.* The fact 

 too that we must look to geology, to ascertain those natural 

 sources of fertility, which are so abundant and desirable in 

 every country, renders some knowledge of this science abso- 



* Dr. Dana in his Muck Manual, p. 20, has given as the third prin- 

 ciple of agricultural chemistry, that " the rocks have not formed the 

 soil which covers them." This appears to be true in a restricted and 

 modified sense. The soil has been moved in most cases from the rock 

 in place, but not alwaj'^s beyond the formation. There are many 

 cases, where the soil is found to have originated directly from the de- 

 cay of the underlaying rock. The second principle, " that rocks do 

 not affect the vegetation which covers them," p. 11, seems to require 

 a similar modification. There are many exceptions to the rule, and 

 the truth would be as nearly expressed if the negative were left out. 

 A case now occurs to me of the marked influence of the underlaying 

 rock. There is a small belt of land in the southern part of Vermont, 

 in which one ingredient is silicate of lime, and the vegetation is not 

 only more flourishing in this formation, but the sweet grasses as clover 

 are much more abundant, although the situation is high, and it is 

 otherwise more unfavorable than the neighboring soils, which are less 

 fertile. Hence, the first principle, that " there is one rock and conse- 

 quently one soil," appears to be opposed, not only to the general opin- 

 ion of writers on soils, but to direct observation. 



