116 AMERICAN MANURES. 



is effected by the infiltration of some substance 

 in solution. These are the freestones, red-sand- 

 stones, etc. Most sandstones are easily dis- 

 integrated by the elements, and form soils 

 rapidly, the value of which is governed by the 

 constituent elements of the stone. 



Soils are named from the relative proportions 

 of their constituents. One hundred parts of dry 

 ordinary soil, containing only ten of clay, would 

 be termed a sandy soil. If it contained from 

 ten to thirty or forty parts of clay, it would be 

 d sandy loam ; if -from forty to seventy parts of 

 clay, it would be a loamy soil ; from seventy to 

 eighty-five of clay, a clay loam ; from eighty-five 

 to ninety of clay, a strong clay., fit for making 

 bricks ; if it contains no sand it would be pure 

 agricultural clay, or pipe-clay. If a soil contains 

 more than five per cent, of lime, it is termed a 

 marly soil ; if more than twenty per cent., a 

 calcareous soil. The rust of iron forms two or 

 three per cent, of most sandy soils, and in red 

 soils much more. 



Farmers must have noticed that some soils 

 assume a darker color or deeper red, under 

 cultivation. These soils contain a large amount 

 of the first oxide of iron, which is injurious to 

 vegetation. The frequent exposure of such soils 

 to the oxygen of the atmosphere, changes this 

 fk*st oxide to the peroxide, as previously stated. 



