4 
SOILS AND ALKALI. 
the region of perpetual snow the surface of the mountain 
masses is covered with rocks in a disintegrated state, in 
greater abundance than below the snow line. Chemical 
action plays an important part in soil formation. It 
manifests itself on a large scale in the formation of vari¬ 
ous mineral species. Some of the older rocks cleave 
freely in planes not parallel with the stratification, and 
possibly mineral veins may be due to the same cause. By 
the instrumentality of organic agency—aqueous, aqueo- 
glacial and igneous action—extending down through the 
ages, the rocks have been transformed into soil. The 
operation is to-day practically illustrated by the trans¬ 
formation of solidified lava from recent volcanic eruption 
into a plant-supporting soil. Geology teaches that the 
earth was once a molten mass, that it has cooled by the 
radiation of heat and become igneous rock. Through the 
agencies of the causes before mentioned, it begins to dis¬ 
integrate ; and soon the simplest forms of microscopic 
vegetable life appear, that find ail the}^ require upon their 
rocky home and the atmosphere; these, when they have 
served their purpose, finally die. The remains of these 
organisms accumulate upon the inhospitable home where 
the plants flourished. This is continued for generations, 
until the accumulated organic matter has covered the rock 
mass and transformed it into soil. The quantity of 
organic matter absolutely necessary as a constituent of 
soils for the production of plants is very small. Peat may 
contain 70 per cent, of organic matter, prairie and gar¬ 
dens 25 per cent. The Mississippi bottoms have about 10 
per cent.; the average of good land is not over 6 per 
cent. Most crops are produced upon soils containing far 
less. 
Oats, rye and buckwheat thrive with the lowest 
amount of organic matter, requiring from 1 to 2 per cent. 
Wheat and tobacco seem to require most among the com- 
