22 SOILS. 



ciple. Alumina stands next on the list in its degree of ab- 

 sorbing power next, carbonate of lime; and least of all, 

 silicia* Hence there ought to be a general correspondence 

 between the absorbing power of a soil and its fertility; and, 

 therefore, this property affords some assistance in estimating 

 the value of a soil. 



When we extend, then, the range of our observation to dif- 

 ferent or distant countries, we see that the nature of the plants 

 cannot indicate that of the soils on which they grow. It is 

 only within narrow limits, and under given conditions of cli- 

 mate, that the kinds of plants afford any certain indication of 

 the nature of the soils which produce them. 



In distinguishing soils, a difficulty frequently occurs in dis- 

 criminating the-pcaty from the earthy. Peaty soils generally 

 lie on a retentive sub-soil; but perhaps the best method of dis- 

 tinguishing them in the absence of their peculiar vegetation, 

 is by the stones which lie upon their surface. These appear 

 to be acted upon by the acid matter of the peat, which, when 

 once observed, will not be easily mistaken again. Coupling 

 this indication with the dull black, as distinguished from the 

 brighter hazel of the loam, and above all, with the peculiar 

 vegetation and sterile aspect of the surface, an observer will 

 soon learn to distinguish the peaty soils from the earthy. 



In examining the earthy soils, an essential circumstance to 

 be regarded is, the depth of the soil, and the texture of the 

 sub-soil. A medium depth of a soil, may be held to be from 

 ten to twelve inches. But it will be better that it exceed a 

 foot, and this greater depth of the soil is always a favourable 

 indication. If the depth of the soil does not exceed six inches, 

 it may be considered as an unfavourable indication. But the 

 staple of such soils, by careful, persevering and judicious 

 management, may be greatly improved, and brought to such a 

 state as to rank with those of the most fertile class of soils; 

 but this, in a great measure, depends upon the character of the 

 sub-soil. 



Shallow soils are rarely good, except sometimes when they 

 occur resting on peculiar rocks, as compact limestone, and cer- 

 tain easily decomposed basalts. If a shallow soil shall occur 

 on a retentive clay, or on silicious sand, we may certainly pro- 

 nounce it to be bad. When in the common operations of 

 tillage the plough is constantly turning up a sub-soil very dif- 

 ferent in colour from the upper stratum, that is an unfavourable 

 indication. 



When we find the rain in a furrow of ordinary descent car- 

 rying off the soil, and leaving the sub-soil exposed, that is an 



* See Hitchcock's Economical Geology of Massachusetts. It is replete with 

 interesting facts. 



