84 INFLUENCE OF ANIMAL LIFE ON VEGETATION. 
Influence of Animal Life on Vegetation. 
The influence of wild quadrupeds upon vegetable life has 
been little studied, and not many facts bearing upon it have 
been recorded, but, so far as it is known, it appears to be con- 
they state that ‘‘ nearly every stream between the Pembina and the Athabasca 
—except the large river McLeod—appeared to have been destroyed by the 
agency of the beaver,” and they question whether the vast extent of swampy 
ground in that region ‘‘ has not been brought to this condition by the work 
of beavers who have thus destroyed, by their own labor, the streams neces- 
sary to their own existence.” 
But even here nature provides a remedy, for when the process of ‘‘ consoli- 
dation” referred to in treating of bogs in the first chapter shall have been 
completed, and the forest re-established upon the marshes, the water now dif- 
fused through them will be collected in the lower or more yielding portions, 
cut new channels for their flow, become running brooks, and thus restore the 
ancient aspect of the surface. 
The authors add the curious observation that the beavers of the present 
day seem to be a degenerate race, as they neither fell large trees nor con- 
struct great dams, while their progenitors cut down trees two feet in diam- 
eter and dammed up rivers a hundred feet in width. The change in the habits 
of the beaver is probably due to the diminution of their numbers since the 
introduction of fire-arms, and to the fact that their hydraulic operations are 
more frequently interrupted by the encroachments of man. 
In the valley of the Yellowstone, which has but lately been much visited by 
the white man, Hayden saw stumps of trees thirty inches in diameter which 
had been cut down by beavers.— Geological Survey of Wyoming, p. 185. 
The American beaver closely resembles his Huropean congener, and I believe 
most naturalists now regard them as identical. A difference of species had 
been inferred from a difference in their modes of life, the European animal 
being solitary and not a builder, the American gregarious and constructive. 
But late careful researches in Germany have shown the former existence of 
numerous beaver dams in that country, though the animal, having become too 
rare to form colonies, has of course ceased to attempt works which require 
the co-operation of numerous individuals.—ScuLEIDEN, Liir Baum und Wald, 
Leipzig, 1870, p. 68. 
On the question of identity and on all others relating to this interesting 
animal, see L. H. MorGan’s important monograph, Tie American Beaver and 
his Works, Philadelphia, 1868. Among the many new facts observed by this 
investigator is the construction of canals by the beaver to float trunks and 
branches of trees to his ponds. These canals are sometimes 600 or 700 feet 
long, with a width of two or three feet and a depth of one to one and a half. 
