Ecology of the Cincinnati Region 
169 
If the associations now existing on river bluffs of different exposures 
are compared with one another, it is seen that the relations are similar 
to those found between the associations of the cleared slopes. 
2. Clay bluffs 
Rarely one of the rivers of the region may be seen cutting bluffs in 
deep clay or clay and sand deposits. These are not the low steep banks 
formed where the stream is under-cutting its own flood plan, but high 
bluffs cut in till deposits, or in sandy terraces. 
Eroding bluffs. —The newer bluffs support little vegetation of any 
sort. On banks of stratified sand or clay, some of the bands are usually 
wet, and along these, are a few annuals and young perennials (fig. 
Occasionally, a row of young willows, cotton-woods, and sycamores is 
seen along a wet band, if erosion has not been excessive for a few years. 
The vegetation of the till banks is more scattered than that of the stratified 
deposits. Each year the banks are undermined by floods, and the plants 
that have started are destroyed. At the up-stream part of the cut, where 
active river erosion has ceased, perennials and woody plants advance 
rapidly. Locust is a common pioneer. Occasionally red cedar is the 
first tree to advance, and sometimes these may be seen dotted over the 
face of the bluff (dg. g6). The herbaceous vegetation is composed of 
the common perennials of dry habitats, and a few more characteristic 
herbs— Lepachys pinnata, Siliphium terehinthinaceuni, Lithospermum 
canescens, Euphorbia corollata, and Aster laevis —which in this region are 
confined to very steep dry banks. 
The succession resembles that of the less resistant rock bluffs, but is 
more rapid. The greatest vicissitudes are encountered in the early part 
of the succession because of the instability'of the material. Parts of these 
clay bluffs usually slump each spring, but during the remainder of the 
year, these banks are firm unless interbedded with sand. Slumping plays 
an iniportant part in the clay succession, by bringing down plants from 
above. Thus woody plants may advance not only from the up-stream 
margin of the bluff, but also from slump centers. 
A clay or sand bluff rapidly loses its original steepness, and after the 
ground is shaded, the succession progresses rapidly. Oaks appear on 
relatively young bluffs, and the first forest cover is composed largely of 
oaks (Quercus Mtihlenbergii, Q. alba, and Q. rubra). 
