Nichols: The vegetation of Connecticut 245 



On the whole, the display of Canadian plants in rock ravines 

 is noticeably richer than in any other sort of habitat, with the 

 exception of bogs. Various explanations for this fact may be 

 suggested. In the first place, the atmospheric conditions here 

 are congenial to northern plants. As compared with less protected 

 habitats, the air is more humid, while, especially in summer, the 

 temperature is uniformly lower and less subject to extremes. 

 Moreover, the length of the growing season is presumably shorter 

 than in more open situations. In a Connecticut rock ravine there 

 may thus be reproduced in miniature a type of climate similar to 

 that which in the Canadian Zone prevails over vast areas. In the 

 second place, geological factors are of undoubted significance. As 

 has already been remarked, most rock ravines have remained prac- 

 tically unaltered since glacial times; they represent very ancient 

 plant habitats. It seems probable, therefore, that boreal plants 

 which today are confined to rock ravines may formerly have been 

 much more widely distributed, and that they have been able to 

 persist in their present habitats because of the unusually favorable 

 environmental conditions there afforded. In the same way it is 

 conceivable that the present boreal aspect of the vegetation in 

 rock ravines may be reminiscent of a one-time much more universal 

 aspect of vegetation in this region. 



Ravines in Unconsolidated Rocks 

 The unconsolidated stony materials which form so considerable 

 a portion of the superficial crust of the earth are not commonly 

 designated as rocks. "Yet no line of separation can be drawn 

 between such solid rocks as those into which the sands and muds 

 of distant geological ages have been transformed and the semi- 

 consolidated deposits of more recent times, or the sediments now 

 accumulating."* In the present paper, the term Unconsolidated 

 Rock embraces any uncompacted rock formation, such as sand, 

 gravel, and clay. For the sake of convenience, the word Rock it- 

 self, written without a qualifying adjective, is used in its popular 

 sense to include only consolidated rock formations. 



Distributio?i, Character, and Vegetation of Ravines in Uncon- 

 solidated Rocks. — In Connecticut, ravines of this description are by 



* Barrel!, J. & Loughlin, G. F.. Conn. State Geol. and Nat. History Survey, 

 BuH. 13: 17. 1910. 



