NICHOLS: THE VEGETATION OF CONNECTICUT 247 
rock are smaller in size and are relatively broader and shallower 
than rock ravines. In consequence, the atmospheric conditions 
are seldom as favorable as those of rock ravines, and the vegetation 
rarely equals that of rock ravines*in the high degree of mesophytism 
attained. Soil moisture, as a rule, would seem to be more im- 
portant here in its effect on vegetation than atmospheric humidity. 
The boreal tone which characterizes the vegetation of rock ravines 
is likewise lacking. This would naturally be expected, not only 
on account of the less congenial environmental relations but also 
because of the comparative recency with which ravines in glacial 
deposits have been developed. 
Spring Brooks.—As Cowles* has remarked, {springs and 
spring brooks may be classed with ravine streams, but differ 
from them in the relative absence of erosion phenomena.” They 
might equally well, if not better, be classed with spring swamps,T 
with which they are usually associated. Spring brooks are com- 
mon throughout Connecticut. Perhaps their most familiar floristic 
feature is the fringe of alders (Alnus rugosa, Alnus incana) which 
almost invariably lines their banks. Aside from these, the brook- 
side flora may include any of the species elsewhere cited as charac: 
teristic of spring swamps. 
The Succession of Vegetation during the Development of Ravines 
in Unconsolidated Rocks.—In his treatment of the plant societies 
of the Chicago region, Cowlest has described the development of 
clay ravines and the concomitant sequence of plant associations. 
The following observations are quoted from this work: ‘“Wher- 
ever there is an elevated stretch of land adjoining a body of 
water, such as a lake bluff, one is apt to find excellent examples 
of the beginning of a ravine. Fig. 1 [reproduced in this paper as 
Fic. 4] shows an embryonic ravine of a type which may frequently 
be seen along the clay bluffs. . . . A ravine of this type is essen- 
tially a desert, so far as plant life is concerned. The exposur . to 
wind and to alternations of temperature and moisture is excessive, 
The lack of vegetation, however, is due chiefly to the instability 
of the soil; this instability is particularly great in the case of clay 
bluffs, where the seepage of water causes extensive landslide action. 
* The physiographic ecology of Chicago and vicinity. Bot. Gaz. 31: 98. 1901 
t See Bull. Torrey Club 42: 192, 193. 1915. 
t Op. cit., pp. 86-88. 
