138 
Ohio Biological Survey 
treme. The slopes are gentle (about 10 degrees) ; the soil a stifif bowlder- 
clay. 
The forest association today is mesophytic, but scarcely climax. 
Beech and sugar maple are dominant trees, but with them occur black oak 
(Quercus velutina), white oak (Qiiercus alba), the small-fruited hickory 
(Carya microcarpa), and Sassafras. Only a few remnants of this forest 
association remain upon the uplands. The character of the undergrowth 
is nowhere displayed. 
The contrast between this morainal forest, and the hydrophytic 
forest of the flat upland to which it is adjacent, is striking. The sudden 
change in vegetation, which is so generally found along the geologic boun¬ 
dary between the two drift sheets in this region, is due chiefly to the 
change in topography. The vegetational line is almost as marked as the 
topographic, and is closely related to it; for wherever the topographic line 
is indistinct, the plant associations grade into one another. In places, the 
morainal forest is almost lacking, and the mesophytic or hydrophytic 
forest of the flat uplands to the south (area of Illinoian till) passes indis¬ 
tinctly into the mixed or hydrophytic forest of the rolling Wisconsin till 
plain. 
This distinction between the vegetation of the two drifts is only pos¬ 
sible upon the uplands, whose topography has been changed by the till 
cover. Soil fertility in the two areas is very different, and farms within 
the area of Wisconsin drift are worth about one and one-half times as 
much per acre as those south of its margin. But similar topographic 
situations upon the two areas support similar types of natural vegetation, 
and the differences which can be noticed are due chiefly to the differences 
in the topography. 
7. Margins of uplands; narrow divides. 
In some places, the remnants of the Tertiary peneplain are so small 
or so well drained, that none of the characteristic upland forest associa¬ 
tions are found. Such conditions are to be seen in the vicinity of the 
major streams, especially near the Ohio and along such narrower divides, 
as the Ohio-Licking, upon which Fort Thomas is situated. In these 
places, the multitude of ravines afford rapid surface drainage, and their 
deep valleys have so lowered the water table beneath the upland, that a 
xero-mesophytic habitat is presented. 
The forest association is essentially that of the dryer ravine slopes. 
It is the association of the tops of ravine bluffs, where xerophytic con¬ 
ditions remain the longest. The association is a retrogressive step in the 
