25^5 



COMPOSITION OF SOILS. 



lyses, taken from SprengeVs book on the composition 

 of soils, will serve as examples of the general nature 

 of ordinary soils ; they are examples taken from 

 lands in the north of Germany. 



100,000 100,000 100,000 



667. The nature and quantity of the organic sub- 

 stances in the soil have great influence upon its 

 character and fertility. They act in several ways. 

 By slowly decaying, they present a constant source 

 of carbonic acid, and likewise of ammonia, if they 

 contain nitrogen ; whilst, by rendering the soil open 

 and porous, and at the same time augmenting its ab- 

 sorbent powers, they assist in keeping it uniformly 

 moist. They also increase the means which the soil 

 possesses of absorbing and condensing ammonia and 

 carbonic acid from the air. 



668. It is a remarkable fact, that a mixture of two 

 or three earths, such as lime, silica, and alumina, is 



