d for the surface of the river to be immediately
raised by means of transmitted pressure. A tide wave thus rendered
abrupt has a close analogy, observes Mr. Whewell, to the waves which
curl over and break on a shelving shore.[452]

The Bore which enters the Severn, where the phenomenon is of almost
daily occurrence, is sometimes nine feet high, and at spring-tides
rushes up the estuary with extraordinary rapidity. The finest example
which I have seen of this wave was at Nova Scotia,[453] where the tide
is said to rise in some places seventy feet perpendicular, and to be the
highest in the world. In the large estuary of the Shubenacadie, which
connects with another estuary called the Basin of Mines, itself an
embranchment of the Bay of Fundy, a vast body of water comes rushing up,
with a roaring noise, into a long narrow channel, and while it is
ascending, has all the appearance of pouring down a slope as steep as
that of the celebrated rapids of the St. Lawrence. In picturesque
effect, however, it bears no comparison, for instead of the transparent
green water and snow-white foam of the St. Lawrence, the whole current
of the Shubenacadie is turbid and densely charged with red mud. The same
phenomenon is frequently witnessed in the principal branches of the
Ganges and in the Megna as before mentioned (p. 279). "In the Hoogly,"
says Rennell, "the Bore commences at Hoogly Point, the place where the
river first contracts itself, and is perceptible above Hoogly Town; and
so quick is its motion, that it hardly employs four hours in travelling
from one to the other, though the distance is nearly seventy miles. At
Calcutta it sometimes occasions an instantaneous rise of five feet; and
both here, and in every other part of its track, the boats, on its
approach, immediately quit the shore, and make for safety to the middle
of the river. In the channels, between the islands in the mouth of the
Megna, the height of the Bore is said to exceed twelve feet; and is so
terrific in its appearance, and dangerous in its consequences, that no
boat will venture to pass at spring-tide."[454] These waves may
sometimes cause inundations, undermine cliffs, and still more frequently
sweep away trees and land animals from low shores, so that they may be
carried down, and ultimately imbedded in fluviatile or submarine
deposits.

CURRENTS IN INLAND LAKES AND SEAS.

In such large bodies of water as the North American lakes, the
continuance of a