On the other hand, when the original coast happens to be high, so that the sea is unable to cast up any thing upon it, a gradual, but destructive operation is carried on in a different way. The incessant agitation of the waves wears it away at the bottom, and at length succeeds in undermining it, causing the upper materials to slide and tumble down, and converting the whole elevation into steep sloping bluffs or cliffs. In the progress of this change, the more elevated materials which tumble down into the sea, have their softer parts washed out and carried away by the waves; while the harder parts, continually rolled about in the agitated water, form vast collections of rounded stones and pebbles, and of sand of various degrees of fineness, which at length accumulate into sloping banks or flat 31beaches, and protect the bottoms of the cliffs against farther depredatios.