CAUSES OF FERTILITY. 229 



widely without any apparent effect, provided the texture be 

 continued the same. 



4. The fineness of the earthy ingredients is more impor- 

 tant to fertility, than the proportions in which they exist ; be- 

 cause the power of the soil to absorb water, and of the roots 

 of plants to draw in nourishment, depend upon the fineness 

 of the particles ; hence it is found, that one earthy ingredient 

 may be substituted for another, provided the electrical char- 

 acter of the soil is not changed. If, however, we are sure 

 that a soil contains silica, alumina, lime and oxide of iron, 

 it may be made fertile. We are sure of all but the lime, 

 which exists in a small quantity in all our soils, and may be 

 added generally without fear of injury. 



5. But the most important substances to be attended to 

 are vegetable matters and salts. Without these, soils are ab- 

 solutely barren, however well constituted in their mineral 

 portions. 



6. Fertility depends not upon the quantity of humus, but 

 upon its state. The greater the quantity of soluble geine 

 (humates, crenates and apocrenates), other things being equal, 

 the greater the fertility. 



7. As salts are removed by continued cropping, they must 

 be supplied from the rocks, or from a foreign source; hence 

 their utility as a manure. 



8. It may be inferred, that the best constituted soil contains 

 the various ingredients in about the following proportions : 

 silica 60 parts in 100, alumina 16, lime 3, oxide of iron and 

 manganese 7, soluble geine 4, insoluble geine 5, potash 3, 

 soda 1, magnesia 1. The earthy constituents may vary, but 

 the salts and geine must be from 4 to 10 per cent., or the soil 

 will not produce a bountiful crop. 



9. Finally, those substances which our soils require to en- 

 sure fertility, are within the reach of all our farmers, and there 

 is the best encouragement for all to seek them out and apply 

 them. No excuse can be rendered if their farms do not 



