The streams proved serious obstacles to early traffic. It has
been shown already that the earliest routes of animal or man
sought the watersheds; the trails therefore usually encountered
one stream near its junction with another. At first, of course,
fording was the common method of crossing water, and the most
advantageous fording places were generally found near the mouths
of tributary streams, where bars and islands are frequently
formed and where the water is consequently shallow. When ferries
began to be used, they were usually situated just above or below
the fords; but when the bridge succeeded the ferry, the primitive
bridge builder went back to the old fording place in order to
take advantage of the shallower water, bars, and islands. With
the advent of improved engineering, the character of river banks
and currents was more frequently taken into consideration in
choosing a site for a bridge than was the case in the olden
times, but despite this fact the bridges of today, generally
speaking, span the rivers where the deer or the buffalo splashed
his way across centuries ago.

On the broader streams, where fording was impossible and traffic
was perforce carried by ferry, the canoe and the keel boat of the
earliest days gave way in time to the ordinary "flat" or barge.
At first the obligation of the ferryman to the public, though
recognized by English law, was ignored in America by legislators
and monopolists alike. Men obtained the land on both sides of the
rivers at the crossing places and served the public only at their
own convenience and at their own charges. In many cases, to
encourage the opening of roads or of ferries, national and state
authorities made grants of land on the same principle followed in
later days in the case of Western railroads. Such, for instance,