PORT ECONOMICS
(Queenstown or Cobhe) and elsewhere. River estuaries,
when sufficiently enclosed, also provide very efficient
harbourage, as is the case at Liverpool, where the mouth
of the Mersey has an internal enlargement. New York is
another instance of a commodious river mouth harbour.
Artificial Harbours. In the absence of natural features,
protection for harbours has to be sought by artificial
means. Ports which found themselves sufficiently well
protected in the days of small ships and local sea trade,
have in many cases had to enlarge their accommodation
by outlying extensions in order to meet modern develop-
ments, and, in so doing, have been under the necessity of
providing massive protective works against the onslaught
of tempestuous seas. Thus, at Genoa and Marseilles, there
are coastal indentations which form a nucleus of natural

harbourage, and certainly provide shelter, but only to a
moderate extent. The growth of these ports has exceeded
their natural limits, and has been extended along the
open coast-line, fronting which it has been necessary to
construct massive breakwaters of masonry and concrete.
Naples is another instance where a huge system of frontal
breakwaters has been similarly developed.

In a number of cases, ports have originated on un-
protected shores, and have had to be provided with
harbours which are entirely artificial, as at Madras,
Sunderland and Zeebrugge. Generally, these take the
form of one or two curving arms, springing out from the
shore, with an opening in the latter case between their
outer pierheads or extremities. The area of water thus
enclosed affords a degree of shelter which is more or less
effective, according to the direction of the wind, the width
and arrangement of the entrance. and other factors of the
case.

Failing a proper harbour enclosure, some amount of
protection is often obtainable in a Roadstead, which is a
deep gut, or channel, approximately parallel with the
shore line, and flanked on the seaward side by sandbanks