250 Nichols: The vegetation of Connecticut 



hold true in the future. From a standpoint of present-day plant 

 geography, therefore, the climax vegetation of rock ravines may 

 be looked upon as practically permanent. 



Although the fact cannot be overlooked that ordinarily the plant 

 societies of rock rav'nes are associated with a definite phase of 

 stream development, it should also be recognized that while very 

 commonly the formation of a ravine has been due to the activity 

 of streams which are still operative, this is by no means always 

 the case. There are many rock ravines whose formation cannot 

 be accounted for by contemporaneous factors at all. Often, 

 as in the Devil's Gulch, the streams now present in such 

 ravines can have played little part in their formation. Many 

 streams have been superposed, so to speak, on the topog- 

 raphy. They have found rather than made their channels. Not 

 infrequently, as in the Wolf Den, ravines have been developed in 

 other ways than by stream erosion. It is largely due to the 

 prevalence of this preerosion type of topography, which has been 

 moulded by physiographic forces of the geologic past, that rock 

 ravines are so much more highly developed in the Highlands than 

 in the Lowland. 



River and Stream Bluffs 



The later phases in river activity may be observed along most 

 of the larger streams throughout the state. As the result of 

 lateral cutting, the ravine once present has been replaced by a 

 broad valley. As a ravine widens out, the exposure to wind, sun, 

 and changes of temperature increases, and the moisture content 

 of the slopes is appreciably modified. The elTect of these environ- 

 mental changes on vegetation can be seen by comparing the flora 

 of a river valley with that of a ravine. In a general way, the vege- 

 tation of stream valleys can be treated under two heads: Bluffs 

 and Flood Plains. The term Bluff, as used here, includes not only 

 the relatively steep slopes which frequently demarcate the valley 

 from the upland, but also the gentler slopes which commonly 

 occupy most of the intervening valley floor. In other words, it 

 embraces all parts of the valley which, in contrast to flood plains, 

 have been formed by erosion rather than by deposition. 



The Vegetation of Bluffs in Unconsolidated Rocks. — In the 



