inclined surface. In
certain cases Beavers carry hydraulic science still further. If the
course of the water is not very rapid, they generally make an almost
straight dyke, perpendicular to the two banks, as this is then
sufficient; but if the current is strong, they curve it so that the
convexity is turned up-stream. In this way it is much better fitted to
resist. Thus they do not always act in the same way, but arrange their
actions so as to adapt them to the conditions of the environment.

The embankment being completed, the animals construct their lodges.
Fragments of wood, deprived of the bark, are arranged and united by
clay or mud which the Beavers take from the riverside, transport, mix,
and work with their fore-paws. During a single night they can collect
as much mud at their houses as amounts to some thousands of their
small handfuls. They thus plaster their houses with mud every autumn;
in the winter this freezes as hard as a stone and protects them from
enemies. These cabins form domes from three to four metres in diameter
at the base, and from two to two and a half metres in height. The
floor is on a level with the surface of the artificial pond. A passage
sinks in the earth and opens about one and a half metres below the
level of the water, so that it cannot be closed up by ice during the
severe winters of these regions.

Within, near the entry, the beavers form, with the aid of a partition,
a special compartment to serve as a storehouse, and they there pile up
enormous heaps of nenuphar roots as provisions for the days when ice
and snow will prevent them from barking the young trunks.

A dwelling of this kind may last for three or four years, and the
animal here tranquilly enjoys the fruits of its industry, as long as
man fails to discover the retreat; for the beaver can escape by
swimming from all carnivorous animals excepting, perhaps, the Otter.
During floods the level of the water nearly reaches the hut; if the
inundation is prolonged and the animal runs the risk of being
asphyxiated beneath his dome, it breaks through the upper part with
its teeth and escapes. When the water returns to its bed the beaver
comes back, makes the necessary repairs, and resumes the usual
peaceful course of its life.[109]

[109] The Beaver has been fully studied by Lewis H. Morgan,
_The American Beaver_, 1868. See also Horace T. Martin's
recent work, _Castorologia, or the History and Traditions of