IRRIGATION. 211 



had this frost extracted in a few weeks by snow, but 

 that the ground, 6 inches below the surface, had a 

 temperature of 39 degrees. This slight elevation of 

 temperature was enough to allow the gaseous exha- 

 lation of organic matter, which was found to exceed 

 that of fresh fallen snow, by 20 times. This quantity 

 in snow 3 inches deep, would give per acre 40 lbs., 

 and to this are to be added 5 lbs. of salts. If this 

 geine is not a natural addition in weight, it has under- 

 gone a transformation and become soluble. Besides 

 every inch of fresh fallen snow, actually adds a little 

 of this same matter ; it will not be extravagant to es- 

 timate the total addition of geine at 50 lbs. per acre 

 for the winter. This added to the warming effects 

 of snow, shows that it may have a genial and enrich- 

 ing power on vegetation, independent of its ammo- 

 nia. The old notion of the existence of nitre in 

 snow is not supported by evidence ; but in whatever 

 view we consider the salts of lime, in snow and rain 

 water, it is difficult to believe that carbonate of am- 

 monia exists in atmospheric air. 



287. There are still other sources of manure, or 

 the elements of fertility, which the farmer can com- 

 mand. Among these, are paring and burning, and 

 the ploughing in of green, and dry crops. 



It is not intended to go into the detail of these 



