146 



hundred square miles, it would indicate 179,200 acres, or 280 

 square miles, of sand. 



In an agricultural state like Illinois the economic aspect 

 of snch a body of sand becomes of importance. Farm land on 

 the neighboring uplands is valued at $100 to $150 per acre, and 

 yields good crops of corn and oats — the grains most generally 

 cultivated. A consideral)le part of the sand area also yields 

 excellent grain crops, but in these fields patches of more or less 

 barren or vs^orthless sand often occur. This land is in fact 

 much better adapted to truck crops. Much of the sand is usable 

 only for pasture, and in Mason county ah^ie there are thousands 

 of acres, assessed at a one-hfth valuation of one dollar per acre, 

 which are not used for any purpose. In no other part of central 

 or northern Illinois, except in the larger river-bottoms, are 

 there such extensive tracts of waste land. 



The surface configuration, wind action on .sand, plant-cov- 

 ering, and similar details of this sand area, are described in con- 

 nection with the biological studies which follow. 



OTHER SAND AREAS. 



The remaining sand areas of Illinois are but imperfectly 

 known to me as yet, but a brief statement concerning the 

 principal ones seems desirable. 



The presence of sand in the soil is not sufficient to 

 modify the character of the biota until it becomes so abundant 

 as to affect the physical character of the surface and cause it 

 to drift easily with the wind, when it is called blow-sand. 

 When this point is reached, cultivation becomes difficult, and 

 the land is usually left undisturbed even by pasturage. In ad- 

 dition to the biotic change due directly to the excess of sand, 

 the absence of cultivation favors the development of a rich and 

 varied fauna and flora. A large part of the areas usually 

 mapped as sandy do not reach this extreme stage, and are con- 

 sequently of less interest biologically. 



In the large sand area of the expanded middle section of 

 the lower Illinois valley, blow-sand is of frequent occurrence. 

 The upper section, about tifty-tive miles in length, lying with- 



