94 ILLINOIS STATE ACADEMY OF SCIENCE 



SOME NORTH AND SOUTH STREAM VALLEYS 

 IN ILLINOIS AND THEIR VEGETATION 



George D. Fuller, The University of Chicago, and C. J. 

 Telford, Assistant Illinois State Forester 



A considerable portion of Illinois is characterized by 

 a relative level upland in which streams have cut chan- 

 nels and developed valleys of varying depth and width. 

 This upland has its surface covered with rich dark col- 

 ored soils described by Hopkins and his associates (1) 

 as upland prairie soils under the designations "brown 

 silt loam" and "black silt loam". These soils, consist- 

 ing of loam formed principally from wind-blown mater- 

 ial, have a depth of 3 to 5 feet and are covered with a 

 grassland that has been well described by Sampson (2). 

 In contrast, the stream valleys display soils character- 

 ized as timber soils by the Department of Soil Survey of 

 the State Agricultural Experiment Station and by them 

 called "yellow-gray silt loam", or "upland timber soil". 



The distribution of these soils and the character of 

 their vegetation in LaSalle County has been discussed 

 previously by Fuller and Strausbaugh (3). In this 

 county the prairie soils cover about 80 per cent of the 

 surface, while the timber soils are limited to 12 per 

 cent and are distributed irregularly along the streams. 

 It has also been pointed out (4) that it seems to be cer- 

 tain that all these timber soils were covered originally 

 with forests and that no forests have ever developed 

 upon the prairie soils. In a further attempt to explain 

 the distribution of vegetation, which here seems to be 

 limited by soil conditions, Fuller (5) has emphasized the 

 peculiarities of the distribution of such timber soil 

 along north and south streams, and has shown 

 that the strip on the east side of the stream is 

 almost always the wider and that it often reaches twice 

 the extent of that on the west bank. Such uneven dis- 

 tribution of timber soils and forest is well illustrated 

 along Big Indian Creek, a tributary of the Fox River. 



The explanation usually current for the narrower strip 

 on the west side of the stream is that prairie fires in 



