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158 THE OJJEAN.
ledge of Cordouan is the sole remains) disappeared under the united ravages of the river and the ocean.
But if the sea demolishes on one side, it builds up on the other, and the
destruction of the ancient shores is compensated for by the creation of
new coasts. The clays and limestones torn from the promontories, the
shingle of every kind which is alternately thrown up on the shore and
swept back in the waves, the heaps of shells, the silicious and calcareous
sands formed by the disintegration of all these fragments, are the materials employed by the sea for the construction of its embankment, and the
silting up of its gulfs.
It is on each side of the cliffs or low points worn away by the waves
that the work of reparation commences. Each wave accomplishes a
double work, for in sanping the base of the promontory it loads itself
with fragments wThich it deposits immediately on the neighboring strand;
by the same action it causes the point to retreat, and the shore of the
bay to gain. Thus, owing to two series of apparently contrary results—
the razing of the points and the filling up of the bays—coasts more or
less deeply indented gradually acquire the normal form with gracefully
rounded curves. Whatever be the outline of the primitive coast, each
inflection of the new shore rounds itself like the arc of a .circle from
promontory to promontory. In those places where the ancient coast was
itself semi-circular, the sand or gravel cast up by the billows is deposited
on the beach; but when the coasts are irregular and indented by deep
creeks, the sea simply leaves them and constructs sands or shingle banks
in front of them, which end by becoming the true shore.
The formation of such a breakwater may be explained in a very simple
manner. The waves of the open sea, driven against the shore, first strike
the two capes placed as guardians at the two extremities of the bay;
here they break their force, and are thrown back against the tranquil waters of the bay. Thus arrested in their speed, they deposit the earthy
matters which they hold in suspension, and also the heavier fragments
torn from the neighboring promontories. At the entrance to the fjords of
Scandinavia, of Terra del Fuego, and all the other mountainous countries
with deeply indented shores, the clear and deep water of the open sea only
brings with it a relatively small quantity of debris, and can only form a
submarine bank* from point to point. But along the lower coasts, where
the tide drives before it masses of sand and clay, the ramparts of alluvium constructed by the waves emerge gradually from the bosom of the
waters.
Under the alternate influence of the ebb and flow, the sand and shingle
are gradually deposited against the rocks of the capes, and thus they
form at the entrance of the bay true jetties, the free extremities of which
advance to meet each other. Being elongated unceasingly, the two segments end by uniting midway between the two capes, and thus form a
large arc of a circle, the convexity of which is turned toward the ancient
* Darwin, South America, p. 24.
| Title | The ocean, atmosphere, and life |
| Creator | Reclus, Elisée |
| Publisher | Harper |
| Place of Publication | New York |
| Date | 1873 |
| Language | eng |
| Type | Books/Pamphlets |
| Title | 00000177 |
| Type | Books/Pamphlets |
| Transcript | 158 THE OJJEAN. ledge of Cordouan is the sole remains) disappeared under the united ravages of the river and the ocean. But if the sea demolishes on one side, it builds up on the other, and the destruction of the ancient shores is compensated for by the creation of new coasts. The clays and limestones torn from the promontories, the shingle of every kind which is alternately thrown up on the shore and swept back in the waves, the heaps of shells, the silicious and calcareous sands formed by the disintegration of all these fragments, are the materials employed by the sea for the construction of its embankment, and the silting up of its gulfs. It is on each side of the cliffs or low points worn away by the waves that the work of reparation commences. Each wave accomplishes a double work, for in sanping the base of the promontory it loads itself with fragments wThich it deposits immediately on the neighboring strand; by the same action it causes the point to retreat, and the shore of the bay to gain. Thus, owing to two series of apparently contrary results— the razing of the points and the filling up of the bays—coasts more or less deeply indented gradually acquire the normal form with gracefully rounded curves. Whatever be the outline of the primitive coast, each inflection of the new shore rounds itself like the arc of a .circle from promontory to promontory. In those places where the ancient coast was itself semi-circular, the sand or gravel cast up by the billows is deposited on the beach; but when the coasts are irregular and indented by deep creeks, the sea simply leaves them and constructs sands or shingle banks in front of them, which end by becoming the true shore. The formation of such a breakwater may be explained in a very simple manner. The waves of the open sea, driven against the shore, first strike the two capes placed as guardians at the two extremities of the bay; here they break their force, and are thrown back against the tranquil waters of the bay. Thus arrested in their speed, they deposit the earthy matters which they hold in suspension, and also the heavier fragments torn from the neighboring promontories. At the entrance to the fjords of Scandinavia, of Terra del Fuego, and all the other mountainous countries with deeply indented shores, the clear and deep water of the open sea only brings with it a relatively small quantity of debris, and can only form a submarine bank* from point to point. But along the lower coasts, where the tide drives before it masses of sand and clay, the ramparts of alluvium constructed by the waves emerge gradually from the bosom of the waters. Under the alternate influence of the ebb and flow, the sand and shingle are gradually deposited against the rocks of the capes, and thus they form at the entrance of the bay true jetties, the free extremities of which advance to meet each other. Being elongated unceasingly, the two segments end by uniting midway between the two capes, and thus form a large arc of a circle, the convexity of which is turned toward the ancient * Darwin, South America, p. 24. |
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