The universal geography : earth and its inhabitants

124
THE BEITISH LSLES.
guishes ttis beach ; it is equally regular with respect to the arrangement of the
materials of which it is composed. Its pebbles increase in size as we proceed
from west to east. The sand in the west almost imperceptibly passes over into
pebbles, and in the vicinity of the Isle of Portland these latter give place to
shingle. The fishermen along the coast will inform you that when they land on a
dark night on any part of the beach they can tell, from the size of the pebbles, at
what spot they find themselves. The true explanation of the phenomenon is
this : the tidal current runs strongest from west to east, and its power is greater in
the more open channel, or farthest from the land, while the size of the fragments
which are carried to the east and thrown ashore is largest where the motion of
the water is "most violent.*
To geologists the Isle of Portland offers a peculiarly interesting field of
research, for it is rich in dirt beds containing organic relics of marine origin,
and still exhibits the fossilised remains of a forest which flourished on the
emero-ed oolite rocks. It is probable that not a single one of these fossils will
escape the notice of man, for few rocks are being more extensively utiHsed.
The upper layers are being carried away to be converted into lime, whilst the
lower beds supply a highly valued building stone, which has been largely used
for some of the monumental edifices of London. In recent times most of the stone
quarried on the " island " has been employed in the construction of a breakwater
planned towards the close of the last century, but only commenced in 1847, mainly
with the view of opposing to the French Cherbourg an English Cherbourg of even
greater strength. This prodigious breakwater is the largest work of the kind ever
xmdertaken, for nearly 6,000,000 tons of stone have been sunk in the sea to protect
against winds and waves an artificial harbour having an area of 2,107 acres, where
the largest men-of-war find secure riding-ground. The first portion of the break-
water runs from the shore due east for about 1,800 feet, and serves the inha-
bitants of the island as a promenade. Then comes an opening of 400 feet, beyond
which the main section stretches 6,000 feet in length, terminating in an ironclad
fort armed with the hea^-iest guns. The summit of Verne Hill (495 feet) is crowned
by impregnable fortifications, armed with one hundred and fifty cannon, and this
citadel, supported by numerous batteries, by a fort on !Nothe Hill, near Weymouth,
and by two ironclad forts on the breakwater itself, amply provides for the security
of the harbour. Breakwaters and forts alike have been constructed by convicts, and
this colossal work of modern England, like similar undertakings of ancient Egypt
and Rome, has thus been accomplished by the hands of slaves, t
But though man may modify the aspects of nature by converting an open
bay into a secure harbour, what are his feeble efforts of a day in comparison with
the slow, but incessant erosive action of a single geological period ? Beyond the
island of Portland and the oolitic rocks of the littoral region, the cretaceous
formation extends uninterruptedly as far as SaL'sbury Plain. That " plain "
• I-yell, " Principles of Geology." Prcstwich, at the Institution of Civil Engineers, February 2nd,
1875. Kinahan, Qiiartirhj Journal of the Geological Society, February 1st, 1877.
t The work occupied about a thousand convicts between 1S47 and 1S72, and cost £1,043,000.
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