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. 1 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 6 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, c from the 
! Note on Beaver Dams ( Proc . Boston Soc. Not. Hist., 1869, p. 101, 
et seq .). 
