PRINCIPLES AND METHODS OF SOIL ANALYSIS. 



ON THE DERIVATION AND THE FORMATION OF SOIL. 



All soils are the result of the natural disintegration of the rocks by 

 atmospheric agencies, mingled with decayed vegetable and animal mat- 

 ter in greater or less proportion. If natural agencies, such as glaciers, 

 rain, frost, wind, c., did not come into play and wash and transport 

 the materials of soil to a greater or less distance from their sources, 

 the soil of every locality would be simply the decayed upper surface of 

 the underlying rocks. But in proportion to the slope of the ground and 

 the activity of the agents above mentioned, the soil is transported from 

 higher to lower levels, and in many cases a good soil may be found cov- 

 ering rocks which of themselves would only yield a poor soil. 



COMPOSITION OF THE SOIL. 



Soil is a mixture of sand, either quartzose or feldspathic, clay, carbo- 

 nate of lime, and humus or organic matter, and on the preponderance 

 of one or more of these constituents the usual classifications of soils are 

 based. 



GENERAL CLASSIFICATION OF SOILS. 



Soils are usually classified as sandy, sandy or light loams, loams, clayey 

 loams, heavy or retentive clays, marls, calcareous loams, and peaty soils. 

 This classification has reference chiefly to composition and texture, a 

 special chemical composition, siliceous, calcareous, &c., being necessary 

 for the profitable growth of particular crops, and a certain mechanical 

 texture, friable, porous, &c., suiting best for the permeation of rain and 

 air, and the spreading of the roots of the plant.* 



Loams, which may be considered as typical soils, are a mixture of 

 sand, clay, and humus, which are spoken of as light when the sand 

 predominates and as heavy when the clay is in excess. These terms, 

 light and heavy, do not refer to the actual weight of the soil, but to its 

 tenacity and degree of resistance it offers to the implements used in 

 cultivation. Sandy soils are, in the farmer's seu.se of the word, the 

 lightest of all soils because they are the easiest to work, whilst in actual 

 weight they are the heaviest soils known. Clay, though hard to work 



* Page's Economic Geology. 



