36 



extent that grasses and trees could gain control the sands were anchored. 

 With the destruction of the vegetative cover they resumed their drifting. 

 Forests have a very important place in the land economics of these sandy 

 regions. Solely as protective cover they are justified. As will be shown 

 later, they may also be developed to produce a profit. 



The sandy loams, being fertile are universally cleared. The dune 

 sands are the least fertile of any of the soils of the state. The presence 

 of very moderate quantities of loam or loess greatly improves the quality 

 of the sandy soils, while a very little organic matter in the surface soil 

 binds dune sand. Thus the sandy soils are very sensitive and unstable, 

 reacting disproportionately to very slight changes in physical composition. 

 It follows that improper handling of these soils may not only quickly de- 

 stroy their productivity but also convert them into drifting wastes which 

 menace adjacent areas. 



In Illinois the wind is a more important agent than water in eroding, 

 transporting, and depositing sands. Bare sand washes readily, but such 

 soils are so open that in ordinary rains there is no appreciable surface 

 run-ofif nor consequent erosion. The ground surface in the sandy areas 

 is ordinarily a series of swells and depressions, the gradient of slope is 

 low, and gullying does not occur. Very different conditions arise when 

 the sands are modified by strata of clay or by loess. On these modified 

 soils the run-off increases, yet the high sand content insures good drainage 

 under ordinary conditions. In certain parts of Whiteside and Carroll 

 counties, however, where the slopes are considerable, the modified sands 

 have gullied seriously. Such ravines ordinarily develop during an excep- 

 tionally heavy storm, the process of formation being very rapid. A gully 

 several feet deep often develops in an unbroken field during a single 

 storm. Once started it eats back into the fields. An example of such 

 erosion in 15 years has cut back into a field 125 feet, gouging a ravine 

 100 feet wide and 70 feet deep. Areas as large as twenty acres are so 

 thoroughly gullied that they can not be crossed. (See PI. II for exam- 

 ples.) Ultimately such land reverts to forest. The areas where such 

 erosion occurs aggregate several thousand acres and merit detailed study 

 before attempting to classify the land into agricultural and absolute forest 

 land. 



The effect of wind upon sand is evident in all these sandy regions. 

 Drifting sand forms low hills having a gentle slope on the windward side, 

 and a steep slope to the leeward. The ridges are often in parallel align- 

 ment and move before the wind burying everything in their progression. 

 Covered by vegetation these dunes become fixed. Destruction of the 

 cover results, under certain conditions, in the development of crater-like 

 depressions from which the sand is blown. In extending agriculture into 

 these areas, man has destroyed the cover and initiated a new advance of 

 some dunes previously fixed ; he has also attempted through cover crops 

 and forest plantations to fix sands which are in motion. The desirability 

 of a forest cover on blow sand is apparent, but the site is so unfavorable 

 that forests do not readily establish themselves. Bunch grass and prickly 



