292 A WOED ABOUT MANfTKES. 



rocks or clay. It is composed of the elements of the 

 rocks, together with an intimate admixture of some mineral 

 substances. In limited patches the soil partakes of the 

 character of the formations underneath. Thus, in iron 

 districts, the soil in places shows. the presence, in considera- 

 ble quantities, of iron, making the earth red or brown. In 

 sandstone countries the clay has a quantity of sand overly- 

 ing it, and among the primitive rocks scales of mica glisten 

 on every side. The weight of a cubic foot of thoroughly 

 dried soil averages as follows : 



Siliceous sand 111.3 pounds. 



Calcareous sand 113.6 " 



Sandy clay 97.8 " 



Loamy clay 88.8 " 



Stiff clay 80.3 " 



Slaty marl 112. " 



Fertile mould 68.7 " 



Common arable soil 84.5 " 



Chemists, from the earliest times, have been struck with 

 the great proportion of insoluble to soluble substances in 

 the soil. These insoluble substances will resist the action 

 of acid and alkali in any quantities short of destroying veg- 

 etation. Analysts have strived by the aid of weak solutions of 

 acids and alkilies to effect this, and though the science is by 

 no means perfect, they have succeeded in rendering much 

 inert matter, that has hitherto cumbered the land, into plant 

 food. In an average of many kinds of soil the proportions 

 are, of 



Insoluble matters, 89.305; 



Soluble matters, 2.047 ; 



Phosphate, carbon and sulphate lime, ... 3.160. 



Thus it is seen that, of the great mass of soil, ranging 

 from a few inches to many hundred feet thick, only a very 

 small per cent, is available to vegetation. Further, chemi- 

 cal analysis has also developed the fact that all animal tis- 



