156 AEE SOILS E^s^RICHED, IMPOYERISHED, n. nr. 



that, on the average, the entire mass of a year's growth 

 of all terrestrial vegetation may be considered as taken 

 annually from below the surface, and annually deposited 

 afresh above the surface. Much of the organic or com- 

 bustible part of this growth goes into the atmosphere 

 in the form of gases, to be returned again to the earth 

 in rain. Of the inorganic or incombustible part, or 

 what would be the ashes of animals and plants if burnt, 

 much is washed into the earth by rain, much ploughed 

 in as manure, much washed into the sea with other soil. 

 But, doubtless, much of this extremely ' finely divided 

 matter ' is transported by wind : and although, in bulk, 

 this aerial deposit is a joke to aqueous deposit, its fertilis- 

 ing qualities are great ; and as woods and parts covered 

 with strong vegetation catch a great quantity of it, by 

 comparison, they are enriched, while surrounding lands 

 are denuded, even supposing aqueous denudation and 

 deposit the same in both. So, in dry windy weather, 

 w^hen cultivated lands are thoroughly cleansed, and 

 broken finely for sowing, great quantities, even of soil^ 

 change places by wind, by which exposed spots are 

 impoverished, and sheltered spots enriched. 



Tins denudation of soil is visible ; so is the deposit 

 of leaves. There are spots on which leaves are never 

 allowed to rest, and others which every year catch 

 large quantities. Ponds fill up even in man's short ex- 

 istence, and must be emptied if they are intended to 

 serve as ponds. This happens whether ponds have a 

 run of a stream through them, or a run of rain into 



