240 ILLINOIS ACADEMY OF SCIENCE 



areas by as much as one to several miles, the iindrained 

 fiats are lilvely to be characterized by scattering cotton- 

 woods and occasional elms, rather than by the pin oak as- 

 sociation. 



2. In using the plural form of the noun prairie for up- 

 land inter-stream areas, the writer follows local custom. 

 The term prairie is used by the residents in a physio- 

 graphic rather than a vegetational sense. A prairie is a 

 flat treeless expanse to them, rather than a particular kind 

 of grassland vegetation, and it matters not whether native 

 vegetation remains. Some of these prairies are known 

 locally by individual names. 



3 and 4. The forest area of the western creeks lacks 

 certain tree species of the Embarrass valley and those of 

 eastern creeks, and includes a somewhat higher propor- 

 tion of xerophytic oak forest. A somewhat peculiar forest 

 association is found along the upper stretches of those 

 creeks which head in the upland prairie, especially that of 

 the western border ; this forest type is made up of pin oak 

 and shingle oak, with hickory, post oak and other xero- 

 phytic trees in admixture. 



5. The out wash plains on the lower side of the Wiscon- 

 sin moraine, in the northern part of the county, were gen- 

 erally covered by a mixed forest, still preserved in many 

 small areas, in which elm is the most abundant species. 

 Other trees are shagbark hickory (Carya ovata), white 

 oak (Q Kerens alba), shingle oak (Qiiercus imhricaria), 

 black walnut (Juglans nigra), and white ash (Fraxinus 

 americana). The northern part of this outwash surface 

 is better drained than the southern fringe, which merges 

 into the prairie uplands of the older glaciation. It would 

 appear from such field studies as have been made that 

 there is consequently a transition in floristic (and eco- 

 logic ) character of the forests of the moraine from its 

 higher parts southward to the base of its outwash ; on the 

 higher parts the white oak-hickory forest is typically 

 developed ; on the outwash slope white oaks become fewer 

 toward the south, and elm, shingle oak, ash and honey 

 locust (Gleditsia triacanthos) become progressively more 

 numerous. This transition requires additional study. 



