196 



deeper sands are always moist, — in the Illinois valley only a 

 few inches below the dry surface layer. 



Much of the blow-sand is a remnant of the greater areas 

 which existed before vegetation invaded these sands. There 

 is little doubt, however, that attempts on the part of man to 

 cultivate or pasture the vegetation-covered sand land have in 

 many cases resulted disastrously and renewed the drifting ac- 

 tion, the destruction of the plant-cover giving the wind a 

 chance to cut in and set the sand in motion again, starting, as 

 it were, an open sore on the face of nature. For this reason 

 large tracts of such land have never been disturbed, and still 

 retain their original flora and fauna; and other fields, after at- 

 tempts at cultivation, have been allowed to go to waste. The 

 processes for the redemption of sandy land now being devised 

 by the United States government should be utilized here, at 

 least to keep this sand where it is and prevent its invasion of 

 cultivable ground. These wind excavations are called blow- 

 outs (PI. VIII., IX. i, and if large enough they soon become the 

 windward side of an advancing dune (PI. XL). Usually they 

 are rounded pits, sometimes large enough to contain a house, 

 the shifting slopes barren of vegetation, and the marginal veg- 

 etation being undermined and swept away. When their depth 

 becomes excessive, moisture at the bottom checks the wind 

 action at this point, and a flora and fauna approximating 

 the ordinary prairie type takes possession of this part of the 

 blowout. The sand from blowouts may pile up in a barren 

 dune or ridge, over the crest of which it drifts in a fine mist 

 with every wind, thus steadily advancing and burying the small- 

 er trees and bushes in its path (PI. X.; XII., Fig. 2); or it may 

 scatter out over comparatively level areas ( PI. XIII.). Clumps 

 of trees or small groves, by checking the wind and thus favor- 

 ing the deposition of sand, occasion the formation of an active 

 dune surrounding them on their windward side, which at least 

 partially submerges them in the course of time (PI. XX., Fig. 2). 



At the earliest opportunity, however, a growth of vegeta- 

 tion, scanty at first, tries to take possession of all blow-sand 

 areas, thus tending to stay the drifting and to fix the surface 



