116 J. E. CRIBBS 



flora in the rocky ravine is commonly associated with a lower 

 water content of the soil than is found in those bearing the 

 evergreens. A large number of species and a large number of 

 individuals of each, is a striking feature of the deciduous type 

 as compared to the relatively few species found in the evergreen 

 stages. Then too, there are generally but six or eight species 

 which are very abundant in the latter type, the others being of 

 less frequent occurrence; while a large number are strongly 

 represented in the former. 



The most important members of this stage include Sassafras 

 variifolia, Tilia americana, Fraxinus americana, Acer ruhrum, 

 Ruhus odorata, Quercus rubra, Primus serotina, Betula lutea, 

 Betula lenta, Ulmus americana, Hamamelis virginiana, Acer 

 spicatum, Viburnum acerifolium, Samhucus racemosa, Magnolia 

 acuminata, etc. 



Of the herbaceous representatives there is a large number, but 

 since a considerable part of these are also associated with the 

 mesophytic woods of the uplands and the floodplains, it will 

 suffice to note at this point some of those which are most 

 typical. These would include Aspidium spinulosum, Aspidium 

 marginale, Polystichum acrostichoides , Aspidium Goldieanum 

 (rare), Asplenium angustifolium {rare), Asplenium Filix-foemina, 

 Asplenium acrostichoides, Dicksonia punctilohula, Chimaphila 

 umbellata, Cypripedium acaule, Cypripedium parviflorum, Ari- 

 saema triphyllum, Pilea pumila, Camptosorus rhizophyllus (rare), 

 Osmunda cinnamomea, Osmunda Claytoniana, Polypodium vul- 

 gare, Psedera quinquefolia, Vitis cordifolia, and Impatiens hiflora. 

 The fern members represented here are seen to be numerous — a 

 feature characteristic of the broad ravine with a deciduous flora. 



The Clay Ravine 



One of the most striking differences between the rocky and 

 clay ravines occurs during the initial stages. The relative 

 instability of the latter does not admit of the formation of ver- 

 tical slopes. During the thawing in spring, and the period of 

 heavy rains which follows, there may be extremely rapid erosion 



