FERTILISING EFFECT OF BOG SOIL AND MUD. 99 



contained in the water, from wliicli they are deposited. 

 This, perhaps, exphiins the difference in the fertihsing 

 eJBTects of the waters used for irrigating meadows, wliich 

 must necessarily vary very much according to the source 

 of the water ; that which has collected on hills covered 

 with a rich vegetation, or has been derived from over- 

 flowing stagnant pools, will doubtless convey maniuring 

 matters to the meadow-lands ; whilst water flowing from 

 bare mountains cannot, in this particular respect, exert 

 any action upon the increase of the grass crop. If such 

 increase takes place notwithstanding, the cause must be 

 sought elsewhere. 



In many places bog-soil, and the mud from ditches, 

 stagnant waters and ponds, are highly esteemed as 

 fertilising agents ; and their influence is explained by the 

 fact, that their smallest particles are saturated with 

 manuring matters, or elements of the food of plants. 

 The same remark appHes to the fertihty of many tracts 

 of cleared wood-land, where the soil for forty or eighty 

 years, or even longer, has received from the layer of 

 foHage and vegetable remains decaying on it, a certain 

 supply of ash-constituents, drawn from a great depth, 

 which are retained by the upper layers of the porous soil, 

 and serve to enrich it. 



The injury done to wood-lands by raking away the 

 leaves cannot be explained merely upon the assumption 

 that the soil is deprived of its ash constituents, which are 

 taken away ^vith the foliage ; for, in themselves, the fallen 

 leaves and twigs are poor in nutritive substances, especially 

 potash and phosphoric acid ; and besides, these elements 

 do not reach the deeper layers of the soil, where they 

 might be again a]3sorbed by the roots. The injury is, 

 perhaps, rather attributable to the fact, that the remains of 

 leaves and plants constitute a lasting source of carbonic 



H 2 



