236 
Hydrangea arborescens Hepatica acutiloba 
*Eupatorium urticefolium Arisema triphyllum 
*Impatiens biflora Botrychium virginianum 
Impatiens pallida Botrychium ternatum 
*Galium spp. Adiantum pedatum 
*Viola cucullata Polystichum acrostichoides 
Aralia racemosa Asplenium augustifolium 
In addition to the species indicated by asterisks, Quercus prinus and 
Sedum ternatum are prominent members of the vegetation of this stage of 
the bluffs. 
Several narrow terraces occur along the sides of the gorge at various 
points. They vary in width from a few feet to as much as 200 feet, and 
one of these, on the east side of the river near the bridge at Test’s Mills. 
is about half a mile in length. The origin of these was not investigated. 
Rejuvenescence, that is, a return to pioneer conditions, may occur at 
any stage of the succession, if erosion of the base of the cliff is resumed by 
the river. In this case, the undercutting by the stream produces slumping, 
and the bare rock wall is soon exposed. ‘This condition occurs at the foot 
of the east bluff, just below the small islands at the lower fall line. At 
this point the bluff had become mesophytic before erosion of the foot began 
again. We have here at the present time an extremely xerophytie bare 
rock face bordering directly upon a mesophytic forest. This xerophytic 
condition will continue as long as the stream erosion continues, and its 
area may even increase. When erosion ceases, the succession will begin 
again, and progress through the stages just described. 
The ravines entering the gorge are small and comparatively few in 
number. ‘The fact that the gorge is relatively young explains this in 
part. The smallness of the area draining into the gorge at this point is 
probably the principal factor, however. Clear Creek parallels the river 
on the west, and the divide between the two streams is less than half a 
mile west of the river. On the east, another small stream parallels the 
gorge at an even less distance. Accordingly the drainage of the area 
immediately around the gorge is largely accomplished by parallel streams 
which enter the river farther down. With two exceptions, the ravines 
are less than 200 yards in length, and are accordingly very steep. These 
two ravines have permanent streams, fed by springs. In the others, the 
rocks drip with seepage, but streams run through them only after rains. 
