384 ANIMAL INTELLIGENCE. 



I must not, however, conclude this epitome of the 

 facts without alluding to the only other publication on the 

 habits of the beaver which is of distinctly scientific value. 

 This is a short but interesting paper by Prof. Alexander 

 Agassiz.^ He says that the largest dam he has himself seen 

 measured 650 feet in length, and 3^ feet in height, with 

 a small number of lodges in the vicinity of the pond. The 

 number of lodges is always thus very small in proportion 

 to the size of the dam, the greatest number of lodges 

 that he has observed upon one pond being five. It is 

 evident from this that beavers are not really gregarious in 

 their habits, and that their dams and canals ' are the work 

 of a comparatively small number of animals ; but to make 

 up for the numbers the work of succeeding inhabitants of 

 any one pond must have been carried on for centuries to 

 accomplish the gigantic results we find in some localities.' 



In once case Prof. Agassiz obtained what may be termed 

 . geological evidence of the truth of an opinion advanced 

 by Mr. Morgan, that beaver-works may be hundreds if 

 not thousands of years in course of continuous forma- 

 tion. For the purpose of obtaining a secure foundation 

 for a mill dam erected above a beaver dam, it was neces- 

 sary to clear away the soil from the bottom of the beaver 

 pond. This soil was found to be a peat bog. A trench 

 was dug into the peat 12 feet wide by 1,200 feet long, 

 and 9 feet deep ; all the way along this trench old stumps 

 of trees were found at various depths, some still bearing 

 marks of having been gnawed by beavers' teeth. Agassiz 

 calculated the growth of the bog as about a foot per cen- 

 tury, so that here we have tolerably accurate evidence of 

 an existing beaver dam being somewhere about a thousand 

 years old. 



The gradual growth of these enormous dams has the 

 effect of greatly altering the configuration of the country 

 where they occur. By taking levels from dams towards 

 the sources of streams on which they occur, Agassiz was 

 able ideally to reconstruct the original landscape before 

 the growth of the dams, and he found that, * from the 



1 Note on Beaver Dams {^Proc. Boston Sac. J^at. Hist., 1869, p. 101, 

 et seq.). 



