breadth, stretching across the whole entrance of the ancient
estuary, and obstructing the ingress of the tides so completely, that
they are only admitted by the narrow passage which the river keeps open,
and which has gradually shifted several miles to the south. The ordinary
tides at the river's mouth rise, at present, only to the height, of
three or four feet, the spring tides to about eight or nine.

By the exclusion of the sea, thousands of acres in the interior have
become cultivated lands; and, exclusive of smaller pools, upwards of
sixty freshwater lakes have been formed, varying in depth from fifteen
to thirty feet, and in extent from one acre to twelve hundred.[407] The
Yare, and other rivers, frequently communicate with these sheets of
water; and thus they are liable to be filled up gradually with
lacustrine and fluviatile deposits, and to be converted into land
covered with forests. Yet it must not be imagined, that the acquisition
of new land fit for cultivation in Norfolk and Suffolk indicates any
permanent growth of the eastern limits of our island to compensate its
reiterated losses. No _delta_ can form on such a shore.

Immediately off Yarmouth, and parallel to the shore, is a great range of
sand-banks, the shape of which varies slowly from year to year, and
often suddenly after great storms. Captain Hewitt, R. N., found in these
banks, in 1836, a broad channel sixty-five feet deep, where there was
only a depth of four feet during a prior survey in 1822. The sea had
excavated to the depth of sixty feet in the course of fourteen years, or
perhaps a shorter period. The new channel thus formed serves at present
(1838), for the entrance of ships into Yarmouth Roads; and the magnitude
of this change shows how easily a new set of the waves and currents
might endanger the submergence of the land gained within the ancient
estuary of the Yare.

That great banks should be thrown across the mouths of estuaries on our
eastern coast, where there is not a large body of river-water to
maintain an open channel, is perfectly intelligible, when we bear in
mind that the marine current, sweeping along the coast, is charged with
the materials of wasting cliffs, and ready to form a bar anywhere the
instant its course is interrupted or checked by any opposing stream. The
mouth of the Yare has been, within the last five centuries, diverted
about four miles to the south. In like manner it is evident that, at
some remote period