deep submarine valley occurs,
called the "swatch of no ground," about fifteen miles in diameter, where
soundings of 180, and even 300, fathoms fail to reach the bottom. (See
map, p. 275.) This phenomenon is the more extraordinary, since the
depression runs north to within five miles of the line of shoals; and
not only do the waters charged with sediment pass over it continually,
but, during the monsoons, the sea, loaded with mud and sand, is beaten
back in that direction towards the delta. As the mud is known to extend
for eighty miles farther into the gulf, an enormous thickness of matter
must have been deposited in "the swatch." We may conclude, therefore,
either that the original depth of this part of the Bay of Bengal was
excessive, or that subsidences have occurred in modern times. The latter
conjecture is the less improbable, as the whole area of the delta has
been convulsed in the historical era by earthquakes, and actual
subsidences have taken place in the neighboring coast of Chittagong,
while "the swatch" lies not far from the volcanic band which connects
Sumatra, Barren Island, and Ramree.[372]

Opposite the mouth of the Hoogly river, and immediately south of Saugor
Island, four miles from the nearest land of the delta, a new islet was
formed about twenty years ago, called Edmonstone Island, on the centre
of which a beacon was erected as a landmark in 1817. In 1818 the island
had become two miles long and half a mile broad, and was covered with
vegetation and shrubs. Some houses were then built upon it, and in 1820
it was used as a pilot station. The severe gale of 1823 divided it into
two parts, and so reduced its size as to leave the beacon standing out
in the sea, where, after remaining seven years, it was washed away. The
islet in 1836 had been converted by successive storms into a sand-bank,
half a mile long, on which a sea-mark was placed.

Although there is evidence of gain at some points, the general progress
of the coast is very slow; for the tides, when the river water is low,
are actively employed in removing alluvial matter. In the Sunderbunds
the usual rise and fall of the tides is no more than eight feet, but, on
the east side of the delta, Dr. Hooker observed, in the winter of 1851,
a rise of from sixty to eighty feet, producing among the islands at the
mouths of the Megna and Fenny rivers, a lofty wave or "bore" as they
ascend, and causing the river water to be ponded back, and then to sweep