664 Harshberger : Plant formations of Nockamixon Rocks 



talus slope with the tree growth and other vegetation, which 

 typically covers the crest slopes above the precipitous rocks below. 

 All along the cliffs just back of the crest slope are cultivated fields 

 where the gullies cut back into the tableland, so that the crest 

 flora forms a narrow fringe which is continuous with the slopes 

 that gradually dip to the precipices below. The soil of these slopes 

 (figures 3 and 5) is edaphically dry and the tree vegetation is con- 

 ditioned largely by the character of the underlying substratum. 



Facies : The steeper slopes where the crest flora is most typ- 

 ically developed are occupied by Quercus Priniis (the most abun- 

 dant tree), Ulviiis ajiiericana^ Ostrya tnrgbiiana, Acer Sacchariun^ 

 Quercus rubra, RJiododendron maximum (on the steepest slopes). 



The rocks which jut out beyond the general crest (figure 5) 

 and from which the escarpment falls abruptly to the river below 

 are tenanted by such trees as Quercus ruhra^ Q. tinctoria (Q. velu- 

 tina), Q, Prinus, Ostrya virgbnanay Betid a lenta^ Cor mis Jlorida, 

 and at the extreme edge are found wind-tossed forms of the red 

 ceda.r, Jioiiperus virgiiiiana. Perhaps such vegetation should be in- 

 cluded as a part of the Rock-Cliff Formation, later to be described. 

 Before considering that formation it should be mentioned that 

 at one point the soil of the tableland is too barren for profitable 

 cultivation of agricultural crops, although the attempt was made 

 years ago to till these barren fields. The abandoned fields are 



Junip 



over 



in an open formation (park-like); associated with Ceanothns ameri- 

 canus and Rhus typhina, together with various weeds. 



Dominant tree species : Tilia americana, Acer rubniin, Carya 

 alba {Hicoria ovata), Nyssa sylvatica, Sassafras officinalis, Primus 

 serotina, Fraxinus amcricana, Castanea dcntata (rareY Pimis 

 Strobus (rare), and Popuhis grandidentata. 



Secoxdary undergrowth species : The brinks of the preci- 

 pices (figure 3) show masses of the yew, Taxus canadensis, to- 

 gether with Diei-z'illa trifida [D. Lonicera), Gayhisaccia frondosa, 

 G. rcsinosa {G. baccata), Ribcs rubrum, R. rotundifolium, Physo- 

 carpus opulifoUns, and Lonicera grata {L. Caprifolium). In addi- 



Haniamclis 



Celasti 



Staphylea trifolia, Viburnum defitatum, V. pnbe 



