dams at the outlets of lakes. In these cases, those trees, even 
J. D. Dana on the Origin of Prairies. 299 
change which can occur independent of climate in the vegetation of the 
lake margins, swamps, and meadows, both recent and ancient. 
Near Norway I founda lake, one part of which has been gradually 
changing to a bog, and presenting all gradations from the open lake to a 
comparatively dry swamp. Approaching the bog, the water becomes 
shoal and the bottom is composed of black, soft vegetable mud of great 
depth, the surface of the mud supporting a variety of aquati¢ plants in 
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extend downward into the soft mud and water, Both these trees will 
grow wheré their roots, and even the bases of their trunks, are continually 
bathed in water. Farther back in the swamp these two trees becom 
casional white-pine and hemlock; the latter, however, only 
eter of three feet, and the Ash to 15 or 18 inches, in the wettest parts 
The final condition of this kind of swamp may be seen in another 
i istant, where an extensive meadow has been formed by 
erly covered by a forest similar to that described, and some portions still 
remain in the original condition. Other parts that have been neglected 
ick 
ad ina in some parts. On some patches 
id 1s doubtless deeper in so re dense thickets of 
In the same region there is another extensive meadow surrounded by 
high, well defined banks of drift material, often terraced, and forming 
described, while other parts, composed of sandy soil and 
= es : 
There is no evidence that grass ever grew upon any part of it until 
3 man, : 
we a eee lands have been flowed by means of 
I have observed some cases where # 2 
