DECOMPOSITION OF SOIL. 215 



ren sands are worthless, a peat bog is little better ; 

 but a practical illustration of the principles, which 

 have been maintained, is afforded by every sandy 

 knoll, made fertile by spreading swamp muck upon it. 

 This is giving geine to silicates. The very act of 

 exposure, of this swamp muck, has caused an evolu- 

 tion of carbonic acid gas ; that decomposes the sili- 

 cates of potash in the sand ; that potash converts the 

 insoluble into soluble manure, and lo ! a crop. That 

 growing crop, adds its power, to the geine. If all 

 the long series of experiments under Von Voght, in 

 Germany, are to be believed, confirmed as they are 

 by repeated trials by our own agriculturalists, it is 

 not to be doubted, that every inch, of every sand 

 knoll, on every farm may be changed, into a soil, in 

 13 years, of half that number of inches of good 

 mould. 



290. That the cause of fertility, is derived from 

 the decomposing power of the geine, and plants, is 

 evident from the fact, that mere atmospheric expo- 

 sure of rocks, enriches all soil lying near and around 

 them. It has been thought among the inexplicable 

 mysteries, that the soil under an old stone wall, is 

 richer than that a little distance from it. Indepen- 

 dent of its roller action, which has compressed the 

 soil and prevented the aerial escape of its geine, 



