KINDS OF SOILS. 147 
mechanical ingredients, or from other highly obvious 
qualities, 
The distinctions thus established, though very vague 
scientifically considered, are extremely useful for practical 
purposes, and the grounds upon which they rest deserve 
to be carefully reviewed for the purpose of appreciating 
their deficiencies and giving greater precision to the terms 
employed to define them. 
The farmer, speaking of soils, defines them as gravelly, 
sandy, clayey, loamy, calcareous, peaty, ochreous, etc. 
Mechanical Analysis of the Soil.—Before noticing 
these various distinctions in detail, we may appropriately 
study the methods which are employed for separating the 
mechanical ingredients of a soil, It is evident that the 
epithet sandy, for example, should not be applied to a soil 
unless sand be the predominating ingredient; and in or- 
der to apply the term with strict correctness, as well as to 
know how a soil is constituted as regards‘ its mechanical 
elements, it is neccessary to isolate its parts and determine 
their relative quantity. 
Boulders, stones, and pebbles, are of little present or 
immediate value in the soil by way of feeding the plant. 
This function is performed by the finer and especially by 
the finest particles. Mechanical analysis serves therefore 
to compare together different soils, and to give useful in- 
dications of fertility. Simple inspection aided by the feel 
enables one to judge, perhaps, with sufficient accuracy for 
all ordinary practical purposes; but in any serious attempt 
to define a soil precisely, for the purposes of science, its 
mechanical analysis must be made with care. 
Mechanical separation is effected by sifting and wash- 
ing. Sifting serves only to remove the stones and coarse 
sand. By placing the soil in a glass cylinder, adding wa- 
ter, and vigorously agitating for a few moments, then 
letting the whole come to rest, there remains suspended 
in the water a greater or less quantity of matter in a state 
