Ecology of the Cincinnati Region 
125 
It seems evident that the distribution of larger trees was determined 
by the extent and depth (or wetness) of the depression. The horizontal 
succession of large trees accords with the contours. The young ravine 
which now cuts across this depression drains its highest parts. In the 
next generation, mesophytic, and even xero-mesophytic trees will advance 
far into the depression, for the saplings now growing ^beneath the hydro- 
phytic trees are largely mesophytes and xero-mesophytes. Of course, 
saplings of the swamp trees are scattered over the whole depression, but 
the facies of the undergrowth everywhere but in the center is of meso¬ 
phytic nature as evidenced by the presence of such trees as sugar maple 
(Acer saccharum), red elm (Ulmns ftilva), wild cherry (Primus sero- 
tina), and white oak (Querciis alba). The center of the depression 
maintains its swamp character, and saplings of red maple, sour gum, 
and shell-bark hickory far out-number those of the other trees. The 
hydrophytic herbs still persist in every local depression, and commonly 
near the center of the major depression. 
Fig. 6, Diagram representing the two successions in progress in the depression 
shown in Figs. 3, 4, and 5. Horizontal distances represent time interval; 
vertical, progress of succession, toward or away from mesophytism. 
Elimination of depression. —Two agencies in particular are at work 
in the elimination of the depression: one biotic, the gradual accumulation 
of humus, which is slowly building it up; the other topographic, running 
water, which is cutting a ravine across it, and so draining it. The first 
is progressive, tending directly toward mesophytism. The latter is retro- 
