THE FORMATION OF SOIL. 57 



necessarily mingled with such finely broken-up 

 mineral matters a quantity of vegetable humus 

 derived from the decay of successive generations 

 of plants, its formation is rendered still more 

 gradual. 



In wooded districts, where a carpet of decaying 

 leaves covers a large part of the ground during 

 most of the year, the water that soaks into such 

 porous soil naturally contains a larger quantity 

 of carbonic acid than would water that had not 

 previously been passed through such matter. This 

 dissolved carbonic acid, from its chemical action 

 on the ingredients of the rock, greatly aids the 

 water in forming new soil. 



Speaking of the loss of the vegetable mould, 

 gained by the patient accumulation of different 

 generations of plants through passing centuries, 

 M. de Bouville, a Prefect of the lower Alps, in a 

 report to the Government, quoted by Marsh on 

 page 540 of " The Earth as Modified by Human 

 Action," * writes as follows : 



* Eeprinted, by permission, from " The Earth as Modified 

 by Human Action," by George P. Marsh. New York : Scrib- 

 ner, Armstrong & Co., 654 Broadway, New York, 1874. Pp. 

 656. 



