118 J. E. CRIBBS 



inclination of the trees growing there. In the latter instance 

 the ravine may be distinctly mesophytic throughout its his- 

 tory, and in the former instance eventually becomes so. 



In sheltered situations the flora is essentially the same in 

 composition from the early stages to one at which it has at- 

 tained a width of some forty or fifty yards. As compared to 

 the rocky ravine, the soil moisture is generally less and the humus 

 is not so well developed. The latter fact is due to the creep, 

 which is more pronounced here because of the greater regularity 

 of the slope. The development of an evergreen flora is less 

 common than in the former situation, but may occur where 

 there is a distinct seepage of water. 



When compared with the rocky ravine at a similar stage, it is 

 found that the tree representation is much greater, especially 

 as to individuals. When in sheltered places, the species are 

 usually the most mesophytic of the climax forest, and include 

 Tilia americana, Fagus grandifolia, Castanea dentata, Acer 

 ruhrum, Prunus serotina, Magnolia acuninata, Sambucus race- 

 mosa, Quercus rubra, etc. The herbaceous species are in large 

 part similar to those of the rocky ravine also, and show a rich 

 fern assemblage. Additional species which are more typical 

 of the clay ravine are Aspleniu7n platyneuron, Epipactus re- 

 pens, Vaccinium canadense, Pyrola secunda, Aralia nudicaulis, 

 Caulophyllum thalictroides, etc. 



The Valley 



The development of the valley from the broad ravine stage, 

 infers a gradual transition; just as does the development of the 

 broad ravine by the slow process of lateral erosion of the slopes 

 of the narrower stage. The chief change in the factors which 

 constitute the habitat here as compared to those of the broad 

 ravine are: (1) A greater access of winds, (2) Greater exposure 

 to direct sunlight, (3) Lowering of the water table, especially 

 on the upper slopes of the valley. (4) A higher average tem- 

 perature with a lower relative humidity. 



This combination of factors all tend toward the same re- 



