14 AMERICAN AGRICULTURE. 



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. 



Besides these, soils are frequently to be seen, more or less 

 extensive, which possess peculiarities entitling them to a 

 distinct classification, and requiring a treatment, in some 

 respects, different from any others. Such are the prarie 

 soils, which, having been annually burnt over for ages, are 

 highly charged with ashes and the alkaline salts. Such 

 also, are the terre-gras lands in Louisiana, and the brick- 

 mold of the East and West Indies, each of which requires 

 peculiar management in plowing and cultivation. 



OTHER CLASSIFICATIONS OF SOILS. Soils are also dis- 

 tinguished by their tendency to absorb and retain water, 

 gravel ^nd 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 ; 

 by their porosity or adhesiveness ; by their chemical charac- 

 ter, whether silicious, argillaceous or calcareous ; by the 

 quality and nature of the vegetation they sustain ; and lastly, 

 and by far the most important, 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, however 

 minute, will suffice to distinguish each. Some obvious yet 

 simple distinctions, which are usually recognized, must 

 nevertheless be assumed for future reference. For this pur- 

 pose, and to avoid unecessary deviations from what should 

 be a common standard, we shall adopt the arrangements as 

 made by Professor Johnston, which is based principally 

 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 



