82 ANIMAL LIFE AS A GEOLOGICAL AGENCY. 



inliabitants abandon it and build on some virgin brooklet a new 

 citj of the waters.* 



* I find confirmation of my own observations on this point (published in 

 1863) in the North- West Passage by Land of Milton and Cheadle, London, 1865. 

 These travellers observed "a long chain of marshes formed by the damming 

 up of a stream which had now ceased to exist," Chap. X. In Chap. XII. they 

 state that " nearly every stream between the Pembina and the Athabasca — ex- 

 cept the large river McLeod — appeared to have been destroyed by the agency 

 of the beaver," and they question whether the vast extent of swampy groimd 

 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 important 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 com- 

 pleted, and the forest re-established upon the marshes, the water now diffused 

 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 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 diminution of their numbers since the introduction of fire- 

 arms, and to the fact that their hydraulic operations are more frequently inter- 

 rupted 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. 135. 



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 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. — Sckleeden, FUr Baum und Wald, 

 Leipzig, 1870, p. 68. 



From a passage in the Dittamondo of Fazio degli Uberti, L. III., ch. ii., it 

 appears that in the time of that author, about 1360, the beaver of Northern 

 Italy was a constructive animal. Speaking of the beaver of the territory of 



Ferrara, he says : 



" Nei 8Uoi laguni un animal ripara 

 Che ^ bestia e pesce, 11 qual bevero ha nome. 



La casa fa iftcastellata, etc., etc." 



I have been lately informed, on good authority, that the beaver is still some- 

 times found in the Delta of the Po. 

 On the question of identity and on all others relating to this interesting 



