12 AMERICAN AGRICULTURE. 



where penetrate their fissures, thus imperceptibly corroding 

 the solid structures and preparing them for future usefulness 

 as soils. If we add to the above, a peat or vegetable soil, 

 we shall have the material divisions of soils, as distinguished 

 by their texture. 



OTHER CLASSIFICATIONS OF SOILS. Soils are also dis- 

 tinguished by their tendency to absorb and retain water, 

 gravel and sand holding very little, while clay and peat 

 readily absorb and retain a great deal; by their constant satu- 

 ration from perennial springs, which are called springy soils; 

 by the quantity of vegetable and animal matter they contain ; 

 l>j infeir poi\)itj~ ;oji> adhesiveness ; by their chemical charac- 

 ter, '^whether* silicio'us*," argillaceous or calcareous ; by the 

 qual|tj*3i>d-nai0re frf.the' vegetation they sustain ; and lastly, 

 .arkf by*fer.rfie4of>mlpo1>tant, they are distinguished by their 

 fertility or barrenness, the result of the proper adjustment and 

 combination of most of the conditions enumerated. Deserts 

 of sands, layers of rocks, stone or pure gravel, and beds of 

 marl and peat are not soils, though containing many of their 

 most important elements. 



It is apparent to the most casual observer, that soils fre- 

 quently and by almost imperceptible degrees, change from 

 one character to another; and that no classification therefore, 

 however minute, will suffice to distinguish each. Some 

 obvious yet simple distinctions, which are usually recognised, 

 must nevertheless be assumed for future reference. For this 

 purpose, and to avoid unnecessary deviations from what 

 should be a common standard, we shall adopt the arrange- 

 ments as made by Professor Johnston, which is based princi- 

 cipally upon their chemical constituents. 



" 1. Pure clay (pipe-clay) consisting of about 60 of silica 

 and 40 of alumina and oxide of iron, for the most, part chem- 

 ically combined. It allows no silicious sand to subside when 

 diffused through water, and rarely forms any extent of soil. 



" 2. Strongest clay soil (tile-clay, unctuous clay) consists of 

 pure clay mixed wiih f> to 15 pnr cent, of a silicious sand, 

 which can be separated from it by boiling and decantation. 



" 3. Clay loam differs from a clay soil, in allowing from 

 \: .11 HO pr-r cent, of fine wind to be separated from it by 

 washing, as above described. By lliis admixture of sand, its 

 parts are mechanically separated, and hence its freer and 

 more friable nature. 



** 4. A loamy soil deposits from 30 to 60 per cent, of sau.l 

 by mechanical washing. 



