Ecology of the Cincinnati Region 
149 
Thus, with the young ravine, there seems to have come an increase 
in mesophytism of the forest, because of the protection afforded by the 
slopes, which are still too gentle, however, to cause xerophytic conditions. 
But this is only temporary; for, on the steeper parts of the hills, oaks are 
appearing. These indicate that as the stream cuts deeper, and its slopes 
become steeper, the mesophytic forest must change. 
Occasionally on the remnants of the old bottoms, are large sycamores 
(Platanus occidentalis) and bur oaks (Quercus macrocarpa), relicts of a 
former hydrophytic association; but most of the newer vegetation is xero¬ 
phytic. Red elm (Ulmiis fulva), red-fruited thorn (Crataegus mollis), 
locust (Robinia Pseudo-Acacia), and hop hornbeam (Ostrya virginiana) 
grow along the top of the low bluff. The stream is not yet actively cut¬ 
ting, and has some flood plain. Its bed is only full of water after heavy 
rains. Pools remain upon the unequal surfaces of the limestone floor. 
Here, and along the margin of the stream, are found a few hydrophytes—• 
Eupatorium perfoliatuui, Bidens laevis, several species of Polygonum, 
Carex, and Cyperus. 
Third stage. —The stream is now flowing about one hundred feet 
below the level of the upland, and has traversed about one-third of its 
course. Its gradient has materially increased, but is very irregular. For 
the heavier limestone layers of the Maysville are fairly resistant, and so 
the stream must flow for sometimes a hundred feet over the horizontal 
surface of a stratum, before it drops several feet over shale and thin 
limestone layers, to another level stretch. The stream is actively cutting, 
and it is only on the inside of a sharp curve, that any flood plain is being 
built. The higher valley floor has entirely disappeared, and the banks 
rise steeply (10 to 20 degrees) from the water’s edge. 
A xero-mesophytic association whose coming was indicated higher 
up the stream, now occupies the ravine slopes. The valley is open, and 
fairly steep sided; a combination of factors which has produced the xero¬ 
phytic conditions. In sheltered parts of the slopes, as along tributary 
ravines, or on north exposures, a mesophytic association is found. The 
soil is thin, so that occasionally rock ledges, or more often loose slabs of 
limestone are found. On these a few species of lichens occur. But here 
they have little importance in the succession, for soil formation by weath¬ 
ering of the shales is so rapid that even on fresh exposures, herbaceous 
plants and seedlings of trees appear the first year. 
On undercut banks, are shown the earliest stages of the xerophytic 
succession. Carrot (Daucus Carota), parsnip (Pastinaca sativa), sweet 
