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THROUGH THE CAUCASUS TO THE VOLGA
248
and the land there is thickly populated and has
many villages, while that on the other side of the
river, and far to the east, is low and flat with
barren salt-steppes and a scantier population.
As I see it, there can be no doubt that these
characteristic conditions must be set down to the
effect of the earth’s rotation, which in the Northern
Hemisphere, where water is flowing south across
the direction of this rotation, will divert it right
wards to the direction of the flow. This force of
diversion brings it about that the stream in a broad
river will usually be strongest along its right side, 1
and the flowing water will have its greatest erosive
power on this side. It must be borne in mmd that
the power of flowing water to carry off gravel and
stone increases as the rate of flow raised to the
sixth. This means, therefore, that if the rate of flow
is doubled, the water will be able to remove sixty
four times as large bits of gravel and stones. The
river-bed will thus usually be deepest near the right
bank, and the river will wear this bank more than
the left one. In this way the river-bed will tend to
shift all the time to the right. In a fairly flat land,
especially if it is made up of loose layers easy for
the river to wear, such a shifting, therefore, may go
on at a relatively fast rate, and become of great
importance. On the left side of the river there will
then be a low flat land left behind, while the right
bank grows higher and steeper as the river digs its
way into higher land. This shifting of the river-bed
over a plain of loose composition will take an even
course until it is held up by ridges of heavier
1 Cp. F. Nansen, Gjennem Sibirien, 1914, p. 128 f.
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