GEOLOGICAL CHANGES EFFECTED BY THE SEA.
(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]
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.