228 



GEOLOGY AND CHEMISTRY OF SOILS. 



Prof. Hitchcock has shown by an analysis of the soils of 

 Massachusetts, that some of the most productive in the State 

 contain less vegetable matter than those more barren. Al- 

 though the proportion of soluble geine, compared with that 

 which is insoluble is very great, (as these soils are the allu- 

 vial deposits of the Deerfield and Connecticut rivers,) it is 

 chiefly the frie state of the mineral ingredients which will 

 account for their fertility. They must be exhausted much 

 sooner than other less fertile soils, and will of course require 

 a constant supply of vegetable matter, to keep up their fer- 

 tility. 



A continued course of cropping improves the texture of 

 nearly all soils. They gradually become finer, and must be 

 deepened to supply the requisite quantity of decomposable 

 minerals. 



We will close this subject, by a general summary of the 

 principles which have been developed, considered in their 

 practical relations to our soils. 



1. The first general conclusion is, that it is important to 

 the farmer to obtain an exact knowledge of the ingredients 

 of his soil, in order to make the required improvement. If 

 a soil is not productive, analysis will show the reason, and 

 point out the right mode of securing fertility. 



2. Although the mineral ingredients of a soil are far less 

 important than the humus and salts, yet it is well established, 

 that a soil composed wholly or ^^ of s'ilica, lime, alumina or 

 magnesia, is entirely barren, hence sand or clay will not sup- 

 port vegetation. 



3. Two kinds of earth are necessary to the fertility of any 

 soil, viz. silica and alumina. But a soil does not attain its 

 highest degree of fertility, unless there are added small quan- 

 tities of lime, magnesia, oxide of iron and of manganese. At 

 least, three earths are essential to the highest state of fertility. 

 Plants require but a small quantity of these earths to enter in- 

 to their constitution, therefore the proportions may vary 



