_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.
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