PAPERS ON BIOLOGY AND AGRICULTURE 



97 



reasonable for similar erosion phenomena on Long Is- 

 land, and it seems to apply with even greater force in a 

 region where" the upland soil consists, according to 

 authorities quoted, of wind-blown loessial material. We 

 may, therefore, conclude that the prevailing westerly 

 winds are the factor limiting the westerly extent of the 

 forest strips bordering north and south streams in Illi- 

 nois, but they are effective through the transportation 

 of soil material rather than through their influence on 

 the advance of prairie fires. 



Fig. 1. Map of a portion of Little Indian Creek in Adams Township, 

 LaSalle .County, 111., showing 'the original extent of the forests on the 

 "upland timber soil," indicated by broken lines. On either side of the 

 stream, the remnants of the forest, indicated by oblique hatchings and 

 the transects A, B, and C, run from west to east across the stream 

 valley. 



