NATURE AND FORMATION OF SOILS. 33 



minerals, they are far more flourishing in the 

 presence of decaying organic matter. Indeed, 

 their action is believed 1 to hasten the decompo- 

 sition of organic material. So it is that the 

 plant, by its own decomposition, is through 

 these agencies made to contribute to the forma- 

 tion of humus, which is an essential part of true 

 soil. 



(3) VEGETABLE ACCUMULATIONS OR DEPOSITS. 

 Not only living plants exert an influence 

 upon the soil, but when they, die their remains 

 form, though very slowly to be sure, accumula- 

 tions of vegetable matter. 



(#) True soil. Vegetable accumulation is 

 most important as well as most conspicuous as 

 a mantle of true soil, formed from the decayed 

 vegetation in the forests or grass - covered 

 prairies. 



($) Wherever vegetation slowly undergoes 

 decomposition under water carbonaceous accu- 

 mulations are formed. The further decompo- 

 sition proceeds the greater the per cent, of car- 

 bon ; thus results peat, lignite, bituminous, or 

 anthracite coal, according to the stage of de- 

 composition reached. 



(V) In fresh-water lakes and ponds, as well as 

 in the sea, the siliceous cases of microscopic 

 plants known as diatoms form considerable ac- 

 cumulations. 



i. Animal Life. Animals have a twofold 



