CHICAGO AND VICINITT. 



47 



reached even on rock hills, though the probability of this is much 

 greater where the hill is composed of limestone than in the case of 

 sandstone or granite. 



B. The day hill. — Morainic hills are common in the Chicago re- 

 gion, and almost without exception they are covered with a mesophytic 

 forest, in which the dominant trees are usually the white oak {Quercus 



Fig. 2S. — Typical upland clay (morainic) forest at Beverly Hills. The dominant trees here 

 are red oaks {Quercus rubra), XhoMgh a white oak {Q. alba) is shown at the extreme right. 



alba), the red oak [Quercus rubra), and the shell-bark hickory [Carya 

 alba). This is easily the dominant forest type of the Chicago region, 

 and is remarkably characteristic of morainic areas. The soil in. all 

 cases is a glacial clay or till, heterogeneous in composition, but rich in 

 food salts. Of all our plant society life histories these are about the 

 most difficult to unravel, and it is due to the favorable conditions un- 

 der which they have developed. After the continental glacier left this 

 region for the last time, it was doubtless on these low morainic hills 

 that the first mesophytic forests were developed. And they have been 

 developed for so long that almost no traces of their history are 



