Ecology of the Cincinnati Region 
153 
North slopes are always more mesophytic than south slopes of equal 
steepness. In some places, the north side of the stream may be bordered 
by the xero-mesophytic association above described, and the south side 
by a more mesophytic association, in which beech is a secondary species. 
The stream bed is broad, and level reaches of limestone are frequent. 
The margins of the stream are swampy, and in places on the limestone 
floor, are swampy patches where small islands have been built (fig. 24 ). 
Fig. 25. The stream drops suddenly into a narrow gorge of shale. West Fork creek. 
Such places carry a hydrophytic vegetation, which is usually varied. 
Among the plants which may be found here are Echinochloa Criisgalli, 
Leersia oryzoides, Cyperns diandrus, C. escidentus, Eleocharis ovata, 
Typha latifolia, Polygonum hydropiper, P. persicaria, P. pennsylvanica, 
Mentha spieata, M. piperita, and Bidens laevis. 
Fourth stage .—After flowing through this open valley, with its broad 
flat bottom, for a considerable distance (as a rule about two miles), the 
stream drops suddenly into a narrow gorge of shale (hg. 2 y). This is 
