172 BULLETIN NO. VII. 
The beaver is naturally pre-emminently a burrowing animal 
and the lodge is thought to have been derived from a modifi- 
cation of the burrow. Where the burrows have been broken ~ 
into by accident they are frequently repaired with sticks and 
grass, thus imitating a lodge and perhaps suggesting how the 
latter may have originated. 
The burrow is the city of refuge and is always provided 
although the family occupies a lodge. The entrance to these 
burrows is usually from beneath the roots of a tree and the 
adit may be ten or fifteen feet long. The chamber in which it 
terminates is perhaps two feet in diameter. The end of the 
burrow is often protected by a pile of sticks which serves in 
winter to prevent the solidification of snow over the chamber 
and thus excluding the air. Such heaps of sticks may have 
been the introductory step to the formation of the lodge. In 
many regions where beavers are abundant lodges are not found. 
The European variety does not exhibit the architectural 
skill for which ours is noted. 
The lodge seems to be adapted for a brood chamber, and 
varies with its location. It is a dome-shaped structure com- 
posed of poles and earth. The lodge is small at first, and is 
not abandoned at the end of the season, as in the case of the 
muskrat, but is enlarged annually. The cavity within, which 
usually communicates with the exterior by two openings, is 
gradually enlarged, and the lodge receives increments of sticks 
from without. The sticks laid up for winter are used in the 
spring for repairing the lodge and the dam. Each fall the 
lodge is plastered externally with mud, which freezing makes 
it very firm. A large lodge may measure over twenty feet in 
external diameter, and the chamber corresponding, eight feet, 
and a foot and one-half in hight. The floor of the chamber is 
usually near the water’s edge, and is beaten hard. The skill 
displayed in the construction of a lodge is no greater than that. 
of the muskrat; the superiority of the beaver lies in his skill 
in constructing dams and other structures secondary to the 
lodge. Canals and dams constitute the chef d’ouvre of the bea- 
ver. The dam precedes the lodge in the order of formation, 
and is designed to retain the water in the pond selected as the 
site of the lodge at a constant level. The dam, like the lodge, 
is of gradual formation, and is not necessarily the product of 
co-operative industry beyond the limits of a single family. 
Dams are either permeable or compact. The solid dam is pre- 
ferred where the opening is well defined and furnished with 
