C 156 ] 



ceous sand; and the finely divided matter consis- 

 ted of 



Carbonate of lime 28 



Silica 32 



Alumina - - - - 29 



Animal or vegetable matter and moisture 1 1 



Of these soils the last was by far the most, and 

 the first the least, coherent in texture. In all cases 

 the constituent parts of the soil which give tenacity and 

 coherence are the finely divided matters ; and they 

 possess the power of giving those qualities in the 

 highest degree when they contain much alumina. A 

 small quantity of finely divided matter is sufficient to 

 fit a soil for the production of turnips and barley ; and 

 I have seen a tolerable crop of turnips on a soil con- 

 taining 1 1 parts out of 1 2 sand. A much greater pro- 

 portion of sand, however, always produces absolute 

 sterility. The soil of Bagshot heath, which is entire- 

 ly devoid of vegetable covering, contains less than -& 

 of finely divided matter. 400 parts of it, which had 

 been heated red, afforded me 380 parts of coarse sili- 

 ceous sand ; 9 parts of fine siliceous sand, and 1 1 

 parts of impalpable matter which was a mixture of fer- 

 ruginous clay, with carbonate of lime. Vegetable or 

 animal matters, when finely divided, not only give co- 

 herence, but likewise softness and penetrability ; but 

 neither they nor any other part of the soil must be in 

 too great proportion ; and a soil is unproductive if it 

 consist entirely of impalpable matters. 



Pure alumina or silica, pure carbonate of lime, 

 or carbonate of magnesia, are incapable of supporting 

 healthy vegetation. 



