(_From the preceding work_.)
_Why are certain formations called marine?_
Because they result from continual deposits of shingle and sand, as may
be seen on the flat coast of our eastern counties. In this manner, at
Lowestoffe-Ness, as well as at Yarmouth, the sea has erected a series of
natural embankments against itself. The present extent of land thrown up
by the sea, and out of the reach of the highest tides, is nearly three
miles long, projecting from the base of the original cliff to the
distance of 660 yards at the Ness. The respective lines of growth are
indicated by a series of small embankments, perfectly defined. Several
of these ridges have been formed within the memory of men now living. A
rampart of heavy materials is first thrown up by a violent gale from the
north-cast. Sand is subsequently blown over, and consolidates the
shingle, and the process is completed by marine plants taking root and
extending their fibres in a kind of net-work through the mass. In
process of time the surface becomes covered with vegetable mould, and
ultimately, in many cases, is productive of good herbage.[5]
[5] From a Communication to the _Philosophical Magazine_, by Mr.
R. Taylor.
_Why are shingle beaches formed by heavy gales?_
Because every breaker is more or less charged with the materials
composing the beach; the shingles are forced forward as far as the
broken wave can reach, and, in their shock against the beach, drive
others before them that were not held in momentary mechanical suspension
by the breaker. By these means, and particularly at the greatest height
of the tide, the shingles are projected on the land beyond the reach of
the retiring waves: and this great accumulation of land upon beach being
effected at high water, it is clear, the ebb tide cannot deprive the
land of what it has gained. Smaller lines are formed in moderate
weather, to be swept away by heavy gales: hence it would appear, that
the sea was diminishing the beach; but attention will show that the
shingles of the lines so apparently swept away, are but accumulated
elsewhere. How often has our observation of these changes realized the
homely simile of Shakspeare:--
Like as the waves make towards the pebble shore,
So do our minutes hasten to their end;
Each changing place with that which goes before,
In sequent toil all forwards do contend.
_Why is this progressive march of beaches far from rapid?_
Because it can only take place in proportion to the greater power or
duration of one wind to another: moreover, the pebbles become comminuted
in their passage, and thus, the harder can only travel to considerable
distances. Works are sometimes constructed to arrest beaches, either to
protect land behind, or to prevent their passage round pier-heads into
artificial harbours, and thus engineers are practically aware of their
travelling power in direction of certain winds.
_Why are sandy-beaches formed more rapidly than shingle?_
Because the breakers have the same tendency to force sand upon the land
as in the case of shingles; but being so much lighter than the latter,
sand can be transported by coast-tides or currents whose velocity would
be insufficient to move shingles. On the other hand, however, smaller
bodies and forces of water can throw sand on the shore. The _spray_ that
could not transport a pebble can carry sand, and thus it is conveyed far
beyond situations where the reflux of a wave can be felt. This may be
witnessed on some parts of the Sussex coast, as at Worthing. In rough
weather too, the spray of the sea, with heavy rain, carries much sand,
which it deposits on the fronts of houses, as may be seen upon the
return of moderate weather: this effect may be witnessed on the splendid
terraces of the Brighton cliffs, and its destructive working on their
plaster fronts is very evident.
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