114 J. E. CRIBBS 



able for plant development. The talus is present on one side 

 only during the earliest stages of the ravine, the other being 

 occupied by the stream which shifts its position, removing the 

 weathered rock now from one side and now from the other. As 

 the ravine approaches a width of twenty yards, a talus forms 

 on each side and increases in amount as the weathering process 

 continues Upon the moist talus slope develop numerous 

 mesophytic species such as Pilea pumila, Cystopteris bulbifera, 

 Smilacina racemosa, Acer spicatum, Aralia nudicaulis, Acer 

 ruhrum, Tilia americana, Solidago caesia, Impatiens biflora, etc. 



Broad Rocky Ravine 



As a small stream of this sort cuts back it's source, there 

 gradually occurs a widening of the ravine. This comes about 

 through the agency of the underground water, which dissolves 

 out the more soluble portions and causes the rock to break up. 

 This occurs most commonly by their splitting along joint planes. 

 The appearance of shale or less firm rocks beneath may facilitate 

 the process, so that the talus is built up of fine weathered mate- 

 rial, intermingled with which are always found great quantities 

 of large and small rocks. When a ravine of this character has 

 attained a width of from one to two hundred yards, the talus is 

 usually still richly supplied with moisture, and there may appear 

 one of two types of flora, — (1) One dominated by evergreens 

 (2) One dominated by deciduous species. 



Evergreen Type. Of these the evergreen apparently develops 

 when there is an abundance of cold water seeping through the 

 talus from the upper slope. When this stage appears it gener- 

 ally persists until the ravine has developed into an open valley 

 with a width of a quarter of a mile or more. 



The chief members of the broad rocky ravine during the ever- 

 gi'een stage are Tsuga canadensis, Aspidium spinulosum, Lyco- 

 podium lucidulum, Aspidium marginale, Porella, Taxus cana- 

 densis, Lycopodinm obscurum, Tiarella cordifolia, Polystichum 

 acrostichoides, Pinus Strobus, Clintonia borealis, Clintonia umbella- 

 tula, Habenaria orbiculata, Cypripedium parviflorum, Viburnum 

 alnifolium. Viburnum acerifolium, Acer spicatum, Trillium un- 



