limits of high tide. Both rivers carry a heavy freight commerce; the
Hudson has a passenger traffic of several million fares each year.
Nearly every river of the Atlantic coast is navigable to the limit of
high tide or a little beyond. Navigation extends to the point where the
coast-plain joins the foot-hills. Above this limit, called the "Fall
Line," the streams are swift and shallow; below it they are deep and
sluggish. As a result, a chain of important river ports extends along
the Fall Line from Maine to Florida.

River-navigation in Europe in the main is inseparably connected with the
great canal systems. As a rule, the lower parts of the rivers are
navigable for steamboats of light draught. Some of the smaller streams
are made navigable by means of a long steel chain, which is laid along
the bed of the stream; the boat engages the chain by means of heavy
sprocket wheels driven by steam, and thus wind the boat up and down the
river.

Ocean steamers penetrate the Amazon Valley to a distance of one thousand
miles from its mouth; boats of light draught ascend the main stream and
some of its tributaries a thousand miles farther. The Orinoco is
navigable within one hundred miles of Bogota. Light-draught boats ascend
the tributaries of La Plata River a distance of fifteen hundred miles.

The Asian rivers that are important highways of commerce are few in
number. The Amur, Yangtze, Indus, and Cambodia have each considerable
local commerce. The Hugli, a channel in the delta of the Ganges, has a
channel deep enough for ocean steamships. The tributaries of the Lena,
Yenisei, and Ob have been of the greatest service in the commercial
development of northern Asia from the fact that their valleys are both
level and fertile.

Because of a high interior and abrupt slopes, the rivers of Africa are
not suitable for navigation to any considerable extent; the channels are
uncertain and the rivers are interrupted by rapids. The Nile has an
occasional steamboat service as far as the "First Cataract," but in high
water the service is sometimes extended farther. The Kongo has a long
stretch of navigable water, but is interrupted by rapids below Stanley
Pool. Similar conditions obtain in the Zambezi. The lower part of the
Senegal affords good navigation. The Niger has in many respects greater
commercial possibilities than other rivers of Africa. It is navigable to
a distance of three hundred miles.

=Canals.=--Canals easily rank amo