254 
ZOOLOGY, 
artificial pond as a refuge when attacked, as well as a sub^ 
aquatic entrance to their lodges and to their burrows in 
the banks of the streams they inliabit. Beaver dams are 
built at first by a single pair or family, and are added to 
from year to year, and afterwards maintained for centuries 
by constant repairs. They are built of sticks and mud, 
usually curve up stream, with a sloping water-face. Beav- 
ers lay up stores of wood for winter use in the autumn; 
they can gnaw through trees eighteen inches m diameter; 
they work mostly at night. Tiiey often construct artificial 
canals for the transportation of the sticks of wood to their 
lodges. This, in the opinion of Mr. Morgan, " is the 
highest act of intelligerce performed by beavers.'^ When 
ponds do not reach hard-wood trees or ground in which 
they can burrow for safety, they will build canals with 
dams, and so excavate them that they will hold the surface 
drainage. Morgan describes one canal about 161 metres 
(523 feet) long which ''served to bring the occupants of 
the pond into easy connection, by water, with the trees 
that supplied them with food, as well as to relieve them 
from the tedious, and perhaps impossible, task of moving 
their cuttings five hundred feet over uneven ground, unas- 
sisted by any descent.^' Beavers, in swimming, use their 
tail as a scull, and the hind feet being webbed, its propel- 
ling power while swimming is very great. They carry 
small stones and earth with their paws, holding them 
under the throat, and walking on their hind feet. They 
use the tail in moving stones, working it under so as tc 
Fig. 294.— Sewellel or Showt'l. Much reduced. 
