re inferior, in geological position, to the chalk.

The same phenomena are repeated in the Isle of Purbeck, where the line
of vertical chalk forms the projecting promontory of Handfast Point; and
Swanage Bay marks the deep excavation made by the waves in the softer
strata, corresponding to those of Sandown Bay.

_Hurst Castle bank--progressive motion of sea beaches._--Although the
loose pebbles and grains of sand composing any given line of sea-beach
are carried sometimes one way, sometimes another, they have,
nevertheless, an ultimate motion in one particular direction.[425] Their
progress, for example, on the south coast of England, is from west to
east, which is owing partly to the action of the waves driven eastwards
by the prevailing wind, and partly to the current, or the motion of the
general body of water caused by the tides and winds. The force of the
waves gives motion to pebbles which the velocity of the currents alone
would be unable to carry forwards; but as the pebbles are finally
reduced to sand or mud, by continual attrition, they are brought within
the influence of a current; and this cause must determine the course
which the main body of matter derived from wasting cliffs will
eventually take.

It appears, from the observations of Mr. Palmer and others, that if a
pier or groin be erected anywhere on our southern or southeastern coast
to stop the progress of the beach, a heap of shingle soon collects on
the western side of such artificial barriers. The pebbles continue to
accumulate till they rise as high as the pier or groin, after which they
pour over in great numbers during heavy gales.[426]

The western entrance of the Channel, called the Solent, is crossed for
more than two-thirds of its width by the shingle-bank of Hurst Castle,
which is about two miles long, seventy yards broad, and twelve feet
high, presenting an inclined plane to the west. This singular bar
consists of a bed of rounded chalk flints, resting on a submarine
argillaceous base. The flints and a few other pebbles, intermixed, are
derived from the waste of Hordwell, and other cliffs to the westward,
where tertiary strata, capped with a covering of broken chalk flints,
from five to fifty feet thick, are rapidly undermined. In the great
storm of November, 1824, this bank of shingle was moved bodily forwards
for forty yards towards the northeast; and certain piles, which served
to mark the boundaries of two manors, were found after t