MAP8HES OCCASIOKED BY LEAVES. 89 



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 construct great dams, while their progenitors cut down trees 

 two feet in diameter and dammed up rivers a hundred feet in width. 

 The change in the habits of the beaver is probably due to the diminu- 

 tion 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. * 



" The American beaver closely resembles his European 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 Ufe, 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, t 



" On the question of identity, and aU others relating to this interest- 

 ing animal, see L. H. Morgan's important monograph, " The American 

 Beaver and his Works," Philadelphia, 1868. Among the many new 

 facts observed by the investigator is the construction of canals by the 

 beaver to float trunks and branches of trees to his pond. These 

 caoals 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." 



It may be considered by some of my readers that the natural 

 history of beavers can scarcely be considered the meteorological 

 effects of forests. The same may be alleged of aU that is being 

 advanced in this chapter relating to the effects of forests on the 

 humidity of the ground. I deem it proper to treat the subject thus 

 freely, partly with a view to anticipating and obviating objections 

 which may suggest themselves to conclusions drawn, and partly 



* " Geological Survey of Wyoming'' (p. 135). 

 t ScMeiden : » Fur Baum und WaW Leipzig, 1870 (p. 68). 



G 



