234 ILLINOIS ACADEMY OF SCIENCE 



as shown on the map (Figure 2) but they are continuous 

 with a larger forest west of the arbitrary boundary line. 



Along the crests and slopes of the ridges are scattered 

 areas of the xerophytic ridge forest. The land has been 

 cleared along the Gross Point Road leaving only an area 

 north of Winnetka Avenue and a small group of trees 

 south of Central Street, but the forest is more continu- 

 ous along Ridge Avenue and the lake shore in Evanston, 

 where it has been less disturbed. Other isolated areas 

 are found along the lake shore in Winnetka and one V- 

 shaped patch north of the Northwestern University ath- 

 letic field. 



The greater part of the land between the Glenwood 

 and Calumet ridges is occupied by the morainic swamp 

 forest. This covers the western part of the residence 

 section of Evanston and nearly all of Wilmette and 

 Kenilworth and extends into Winnetka. The outlines 

 of the central area are very irregular and there are 

 smaller patches outlying on the east and west. A some- 

 what similar but less extensive forest lies between the 

 Calumet and Tolleston ridges. 



Although the typical sections of the different associa- 

 tions are very dissimilar, there is in certain places a 

 transition from one association to another, so gradual 

 that a line can hardly be drawn between them. Thus a 

 forest area may be classed as one type on the map, when 

 it is apparently intermediate between that type and an- 

 other. Such an area is the one at Winnetka Avenue, 

 west of the Gross Point Road. It is classed as xerophytic 

 because of its location on the slope of the ridge and be- 

 cause the red oaks are more numerous than the whites 

 (Quercus alba). It resembles the xerophytic forest on 

 the Northwestern University campus south of Simpson 

 Street, but is more mesophytic than the other areas of 

 ridge forest in the region studied. The southern and 

 western limit of this area were not determined. 



It is possible also that in such a case the characteristic 

 species have been removed or killed and the resulting 

 type is not the natural one. This is especially likely 

 where the remaining patch is small and the undergrowth 



