160 7 BOTANICAL GAZETTE [MARCH 
is much greater where the hill is composed of limestone than in 
the case of sandstone or granite. 
B. The clay ill—— Morainic hills are common in the Chicago 
region and almost without exception they are covered with a 
mesophytic forest, in which the dominant trees are usually the 


Fic. 28.—Typical upland clay (morainic) forest at Beverly hills. The dominant 
trees here are red oaks (Quercus rubra), though a white oak (Q. a/éa) is shown at the 
extreme right. 
white oak ( Quercus 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 character- 
istic 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 diffi- 
cult to unravel and it is due to the favorable conditions under 
which they have developed. After the continental glacier left 
this region for the last time, it was doubtless on these low 
Sf aa ee 

