, &c.

_Military communications._--The movements of armies are always much
embarrassed by forests, marshes, and water-courses, and nothing
contributes more to the dispatch of military operations than the means
of opening practical and easy communication through these various
obstacles.

It is not necessary here to enter into any detailed discussion of the
manner of constructing military communications through forests or
marshes. In a new country like ours, where almost every one has had some
experience in road-making, no very great technical knowledge is required
for the construction of temporary works of this character; but much
professional skill and experience will be requisite for the engineers
who make the preliminary reconnaissances, and fix the location of these
roads.

Water-courses may be crossed by means of fords, on the ice, or by
ferries and bridges. When temporary bridges or ferries are constructed
by the army in the field, they are classed under the general head of
_military bridges_, or more properly, _pontoniering_.

Where the depth of the stream is not great, the current slight, and the
bottom smooth and hard, the passage may be effected by _fording_. If the
bottom be of mud, or large stones, the passage will be difficult and
dangerous, even where the depth and current are favorable. Under
favorable circumstances infantry can ford a stream where the depth is
not greater than four feet; cavalry to a depth of four or five feet; but
artillery, and engineer trains, cannot go to a depth of more than two
and a half feet, without greatly exposing their ammunition and military
stores The fords should be accurately staked out before the passage is
attempted, and ropes ought to be stretched across the stream, or cavalry
and small boats stationed below, to prevent the loss of life.

Ice may be crossed by infantry, in small detachments. Its strength may
be increased by covering it with boards, or straw, so as to distribute
the weight over a greater surface. By sprinkling water over the straw,
and allowing it to freeze, the mass may be made still more compact. But
large bodies of cavalry, and heavy artillery, cannot venture on the ice
unless it be of great thickness and strength. An army can never trust,
for any length of time, to either fords or ice; if it did a freshet or a
thaw would place it in a most critical state. Military bridges will,
therefore, become its only safe reliance for keeping open its
commu