e, the
level of the great continents, with their table-lands and mountains, is
an ever fluctuating line. It may seem strange that land should be less
stable than water. We see the tide rising and falling twice every
twenty-four hours, and the rock ever remaining in its place;--we speak
of the fixed earth and the unstable sea. And yet, while we have no
evidence whatever that the sea level has changed during at least the
ages of the Tertiary formations, and absolutely know that it could not
have varied more than a few yards, or at most a few fathoms, we have
direct evidence that during that time great mountain chains, many
thousand feet in height, such as the Alps, have arisen from the bottom
of the ocean, and that great continents have sunk beneath it and
disappeared. The larger part of northern Europe and America have been
covered by the sea since our present group of shells began to exist; and
it seems not improbable that the lower portion of the valley of the
Jordan was depressed to its present low level of thirteen hundred feet
beneath the Mediterranean since the times of the deluge. On several
parts of the coasts of Britain and Ireland the voyager can look down
through the clear sea, in depths to which the tide never falls, on the
remains of submerged forests; and it is a demonstrable fact, that even
during the present age there are certain extensive tracts of land which
have sunk beneath the sea level, while certain other extensive tracts
have been elevated over it. In 1819, a wide expanse of country in the
delta of the Indus, containing fully two thousand square miles of flat
meadow, was converted by a sudden depression of the land, accompanied by
an earthquake, into an inland sea; and the tower of a small fort, which
occupied nearly the middle of the sunken area, and on which many of the
inhabitants of a neighboring village succeeded in saving themselves, may
still be seen raising its shattered head over the surface,--the only
object visible in a waste of waters of which the eye fails to determine
the extent. About three years after this event, a tract of country,
interposed between the foot of the Andes and the Pacific, more than
equal in area to all Great Britain, was elevated from two to seven feet
over its former level, and rocks laid bare in the sea, which the pilots
and fishermen of the coast had never before seen. On the Indian coast
the sea _seemed_ to be rising at nearly the same time when it _appeared_
t