236 



Hydrangea arborescens Hepatica aeutiloba 



*Eupatorium urticrefoHum Arisjema triphyllum 



*Impatiens biflora Botrychium virginianum 



Impatiens pallida Botrychium ternatum 



*Galiuin spp. Adiantum pedatum 



♦Viola cucullata Polystiehum acrostichoides 



Aralia racemosa Asplenium augustifolium 



lu addition to the species indicated by asterisks, Quercus priuus and 

 S'edum ternatiun are prominent members of the vegetation of this stage of 

 the bluffs. 



Several narrow terraces occur along the sides of the gorge at various 

 ]>oints. They vary in width from a fev>- feet to as much as 200 feet, and 

 one of these, on the east side of the river near the bridge at Tesfs Mills, 

 is about half a mile in length. The origin of these was not investigated. 



Rejuvenescence, IJiat is, a retium 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 ihe 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 th^ lower fall line. At 

 this point the bluff had become mesophytic before erosion of the foot began 

 again. We have here at the pi-eseiit time an extremely xerophytic bare 

 rock face bordering dirertly upon a mesophytic forest. This xerophytic 

 condition will continue .-ts long as the stream erosion continues, and its 

 area may even increase. When erosion ceases, the succession will begin 

 again, and ))rogreis 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 accoinidished by parallel streams 

 whicli 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. 



