36 



Mississippi Valley. The economic, sociologic, political, and historical 

 significance of the difference in the soils of these regions is funda- 

 mental to any adequate imderstandng of man's response to his ecolog- 

 ical environment within this area. Some of the results of this differ- 

 ence have long been known, but it is only in recent years that their 

 general bearing has been adequately interpreted in terms of the en- 

 vironment. Hubbard ('04) was the first, I believe, to show the sig- 

 nificance of this difference in soils and its influence upon local eco- 

 nomic problems. That such an important influence should affect one 

 animal (man) and not others seems very doubtful, and yet in only one 

 other case do w^e know that the lower animals respond to this ecologic 

 influence. Forbes ('07b) has shown that certain kinds of fish found 

 in streams on the fertile soils are wanting in streams on the poorer 

 soil. To what degree the land fauna and the native vegetation respond 

 to this distinction is not known, as this subject has not been investi- 

 gated except agriculturally. Here, then, is a factor in the physical 

 surroundings which should be reckoned with in any comprehensive 

 study of the biotic environment. In this portion of the state, on ac- 

 count of the differences in the soil, the physical environment is prob- 

 ably more favorable to certain organisms and less favorable to others, 

 and consequently, to a certain degree, the environment selects, or fa- 

 vors, some organisms. Through their activities and through other 

 agencies of dispersal, the animals along the borders betw^een the two 

 soil types transgress these boundaries, and are therefore forced to 

 respond to the new conditions and to adjust themselves, if possible. 



But the soil is not the only environmental influence which has pro- 

 duced an unstable zone or tension line in this area. A second factor is 

 the difference in the vegetation — the difference between the forest and 

 the prairie. In all probability, Coles county was at one time all prairie, 

 but the Kaskaskia and Embarras rivers, as they cut their valleys 

 through the moraine and developed their bottoms, have led forests 

 within the morainic border from farther south. The forests about 

 Charleston have extended from the Wabash River bottoms. On account 

 of the southerly flow of the Embarras through this county, the forest 

 and prairie tension line is about at right angles to that produced by the 

 differences in the soil. The forests have tended to spread east and west 

 from the streams and to encroach upon the prairie, and thus to restrict 

 its area more and more. The fundamental significance of the tension 

 between the forest and the prairie has long been known within the 

 state. It influenced its economic, social, political, and historic develop- 

 ment as much as any other single factor during its early settlement. 

 And just as Hubbard ('04) has shown the influence of soil upon man 



