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 
tock 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. 
Distribution, Character, and Vegetation of Ravines in Uncon- 
solidated Rocks.—In Connecticut, ravines of this description are by 
* Barrell, J. & Loughlin, G. F., Conn. State Geol. and Nat. History Survey, 
Bull. 13: 17. 1910. 
