1909] The 1907 Alexander Alaska Expedition. 253 
but some of the old ones knew what a canoe was and upon 
catching sight of one they would bring their tails down upon the 
water with a pop like the explosion of a fire-cracker, and then 
hastily disappear in the water. We rarely saw a beaver on the 
land, as they carry on most of their work at might. About six 
o’clock in the evening the beavers would begin to come out, but 
they would be back again to their dams or houses by about seven 
in the morning. 
‘*We found that the mode of life of the beavers divided them 
into two classes, bank beavers and house beavers. All of the 
bank beavers that we killed were males and I am inclined to 
believe that they were bachelors, who had gone off to live in 
holes in the banks instead of building houses and raising fam- 
ilies. The houses were usually in some secluded corner of a 
beaver pond in which the water had been backed up by the dams 
that they had built until it suited them. One dam that we saw 
was at least one hundred and fifty yards long, and between four 
and five feet high. (Plate 26.) It was very irregular in shape 
as it curved about so as to keep the erest on the same level. The 
dam was six or eight feet wide at the base and tapered to about 
one foot at the top. Some of the saplings used were six or eight 
feet long and from two to three inches in diameter, but most of 
the sticks were smaller and shorter. After the sticks had been 
worked in and wedged together the beavers had dumped in a lot 
of mud and soil. 
“They carry the mud between their forepaws and the body 
just as Thomomys or similar rodents do. Their dams were not 
eurved against the stream in the majority of cases, although we 
did see some cases where the arch was used to good advantage. 
It seemed to me that the beavers showed their greatest engineer- 
ing skill not in felling trees and constructing dams but in the 
way they dug ditches and canals, forming highways for traffic, 
and in the way they had of distributing the water so that there 
would be just a little water running over the dams all along. 
If the water had not been distributed and had run over in just 
two or three places it would have washed the dam out very soon. 
““The houses were not like the pictures and drawings that we 
sometimes see. They did not look like an old-fashioned brick 
