172 
Ohio Biological Survey 
Up-stream, the bluff decreases in steepness as it becomes older. At 
the same time, the vegetation becomes denser. A young forest made 
up of oaks (Qiierciis Muhlenbergii, Q. rubra, and Q. alba), hackberry, 
redbud, basswood, thorn (Crataegus mollis), hop hornbeam, and red 
cedar, shades the banks. The undergrowth is made up of a few smaller 
saplings, and the shrubs, Rhus canadensis, Physocarpus opidifolius (nine- 
bark), and Cornus asperifolia. The Rhus is by far the most important 
and characteristic of these shrubs, as in this locality it is entirely re¬ 
stricted to such habitats. It often forms large patches to the exclusion 
of other vegetation. The original xerophytic herbs are largely driven 
out, and in their places are Aquilegia canadensis (wild columbine), Pha- 
celia Purshii (Miami mist). Phlox divaricata, Sanguinaria canadensis 
(bloodroot), Arabis canadensis, Silcnc virginica (fire pink), and Aster 
Shortii. The numerous bowlders which lie on the surface are covered 
with lichens and moss. 
Soon a number of marginal trees appear at the foot of the bluff, but 
these belong to the life history of the flood plain which is now being 
built. The bluff succession in progress is entirely independent of this. 
The demarcation between flood plain and bluff is sharp. The original 
xerophytes retain their position at the top of the bluffs long after they 
have disappeared from the slopes. Above the marginal trees at the 
foot of the bluffs, a few mesophytes appear, sugar maple first and then 
beech. 
The terrace retains its steep and bluff-like margin long after the 
food plain has grown wide at its foot, and all stream erosion has ceased. 
The mesophytic tendency displayed on the lower slopes is an indication 
of what the future forest will be. But even the oldest bluff*s show little 
more than a small percentage of mesophytic trees. Oaks predominate, 
and in some places along the Little Miami, red cedar is important. Sugar 
maple saplings are not uncommon, and sometimes flowering dogwood' 
(Cornus dorida) is seen. The herbaceous flora retains much the same 
aspect as on the younger bluffs, but is a little more varied and denser. 
The summer blooming plants are not abundant, for the steep gravel 
slopes are very dry except during the spring when rains are frequent. 
The gravel bluff exhibits many peculiarities not seen on bluffs of 
rock or clay. Under-cutting banks in gravel are even more unstable 
than those in clay; at least as far as the surface layer is concerned, and 
more xerophytic than most rock bluffs. A number of the plants of these 
bluffs fRhus canadensis, Physocarpus opidifolius, Verbena stricta, Kuhnia 
