THE BEAVERS OF NORTH AMERICA 15 
sents what is probably the original and primitive 
form of house. The entrances, for there are usually 
more than one, are well below the surface of the 
water. Then we have the next step in advance- 
ment : the hole in the bank with the living chamber 
coming to the surface, so that in order to make it 
more secure against marauders and render it drier, 
a roughly arranged pile of brush, sticks, logs, and 
mud and grass is heaped over it. From this it 
is but a step to the house which is entirely above 
ground, and placed either on the bank or on an 
island, and then the final development in which the 
beavers make the island as a foundation. 
In appearance, the two latter types are identical 
and both have the entrances beneath the water. 
In building these houses or lodges, as they are more 
commonly called, the beginning is a composition of 
mud, brush and small sticks, from which the bark 
is nearly always eaten. Whether the mound is 
placed over the opening of the burrow, or whether 
the burrow is made after the house has been started, 
I cannot say with absolute certainty, but from 
what I have observed of the beginnings of lodges, 
there seems every reason to believe that the burrow 
precedes the lodge. Gradually, as the mound 
becomes large enough, the inside is hollowed out, 
then more and more material is added to the out- 
side, larger sticks and even poles or logs are used, 
all more or less pointing to the apex, so that they 
support each other to some extent. Water- 
