17 



Sand stones are composed of alumina, silica, iron, carbonate of 

 lime, and other substances in various proportions. In some 

 the particles are cemented together by a kind of semi-fusion, 

 as in the buhr-stone formation, while in others, as the free stones 

 and red sand stones, it is effected by the infiltration of some 

 soluble substance. They are easily disintegrated and rapidly 

 form soils. 



An important constituent of all soils is the vegetable mould, 

 or humus, which must be at least five per cent, of the soil, if it 

 be a fertile one. This humus is the brown, earthy part of the 

 soil, and is the result of the partial decay of leaves, roots and 

 all other parts of plants. The special office of this constituent 

 is mechanical, and it acts by absorbing heat, moisture, and. 

 fertilizing gases from the atmosphere, and storing them for 

 the growing plant; it also affords support to its structure. That 

 the fertility of a soil does not depend directly upon the per- 

 centage of humus has been proven, but up to a certain point it 

 must be present to make a fertile soil. 



In order that the planter may form an idea of different soils, 

 we here arive several analyses of various ones : 



O *J 



