Ecology of the Cincinnati Region 
163 
rock exposed is always largely shale, and therefore the earliest stages 
of rock bluff vegetation are not shown. 
The bluffs of the Ohio rise from 300 to 400 feet above the river, 
gently at first but precipitous above. The steepest bluffs and those 
showing the youngest stages in the succession, are found in the position 
of pre-glacial cols and on the inside of meander curves (Hg. i8). It is 
here that slumping is most effective in producing the bare rock bluffs 
upon which the pioneer associations start. The Bellevue division of the 
Maysville, which is by far the most resistant rock of the formation, 
stands out prominently. It outcrops near the tops of the higher bluffs, 
there forming almost vertical cliffs, fifteen feet high. The slope above 
this is gentle; below, steep as far down as the Eden-Maysville contact 
about 100 feet below, where it changes to a gentler slope on all but the 
youngest bluffs. 
Along the Miami and Little Miami valleys. Mill creek valley, and 
the pre-glacial valleys, are lower rock bluffs, which are seldom as steep 
as the bluffs of the Ohio valley. 
Pioneer herbaceous association. —Except on the most resistant rock 
cliffs, the pioneer vegetation is herbaceous. The only plants are a few 
annuals. The earliest associations in the bluff succession may be com¬ 
pared to those found on abandoned quarry faces. The first plants to 
appear are black mustard (Brassica nigra), sweet clover (Melilotus alba 
and M. officinalis), parsnip (Pastinaca sativa), and Aster eric aides. A 
few years suffice to cover all but the steepest parts with this herbaceous 
growth. The shale, which is everywhere interbedded with the limestone, 
weathers rapidly and soon supplies enough soil for woody plants. 
The first tree stage. —Ability to withstand strong light is apparently 
a factor in determining what trees shall appear. The first are locust 
(Robinia Pseudo-Acacia), honey locust (Gleditsia triacanthos), red elm 
(Ulnius fulva), and blue ash (Fraxinus quadrangulata). With or soon 
after these, are redbud (Cercis canadensis), and red-fruited thorn (Crn^ 
taegns mollis). Sycamores are not uncommon as pioneers, appearing 
in gullies or along horizons of abundant seepage of ground-water. The 
herbaceous plants of the open slopes begin to disappear, and in their 
places come the purple aster (Aster Shortii), cleavers (Galium Aparine), 
motherwort (Leonurus Cardiaca), catnip (Nepeta Cataria), and wild 
onion (Allium cernuum). 
All parts of the slope do not reach this stage with equal rapidity. 
The succession progresses most rapidly upon the gentler slopes below. 
