82 THE SOIL. 



A soil formed by a mixture of clay and sand, in nearly 

 equal proportions, is called a clayey sand or a sandy clay, 

 according as the one or the other predominates. If much 

 more than one-half is clay, we call it a loamy clay. So 

 we call a soil a calcareous clay, or a clayey calcareous soil, 

 as the clay or the lime is the more abundant. 



282. It must, however, always be understood, that all 

 these combined, even in the most favorable proportions, are not 

 sufficient to form a good soil. There must be superadded 

 a certain amount of humus, mould or geine. This seems 

 to be at the same time the reservoir, and often, perhaps, 

 the source, of those saline matters and of a large portion 

 of the nitrogenous and carbonaceous substances which 

 are essential to the growth of plants. 



Humus, or Geine, for both words mean the same thing, 

 is a dark-colored earthy matter, fatty to the feeling, 

 formed from the remains of vegetable substances, and 

 sometimes also animal, in different stages of decomposi 

 tion. It readily attracts and absorbs water and retains it, 

 not only rain water but the vapor of the air. It is the 

 perfection of vegetable earth. Land is considered good 

 arable land, which contains three or four per cent, of it. 

 Soil containing as much as eight per cent, of it, is good 

 garden mould, and with ten per cent, it becomes very 

 rich. 



283. It can be very readily ascertained whether there 

 is any humus present, by burning a quantity of the soil 

 upon a red-hot fire-shovel. As the humus calcines and 

 turns into charcoal, it exhales an odor cither like that of 

 burnt horn or feathers, or like that of burning straw. If 

 the smell 1)0 strong of burnt feathers, it indicates a soil 

 rich in the products of decayed animal substance. If the 



