These river deposits are prevented from advancing further into the sea by the regularity of the ebb and flow, which continually drive them back. For after the manner of living creatures, which go on inhaling and exhaling their breath continually, so the sea in a like way keeps up a constant motion in and out of itself. Any one may observe who stands on the sea-shore when the waves are in motion, the regularity with which they cover, then leave bare, and then again cover up his feet. This agitation of the sea produces a continual movement on its surface, which even when it is most tranquil has considerable force, and so throws all extraneous matters on to the land, and Flings forth the salt weed on the shore.Iliad ix. 7.Iliad ix. 7. This effect is certainly most considerable when the wind is on the water, but it continues when all is hushed, and even when it blows from land the swell is still carried to the shore against the wind, as if by a peculiar motion of the sea itself. To this the verses refer— O'er the rocks that breast the flood Borne turgid, scatter far the showery spray,Being swollen it rises high around the projecting points, and spits from it the foam of the sea. Iliad iv. 425.Iliad iv. 425. and, Loud sounds the roar of waves ejected wide.The lofty shores resound, the wave being ejected [upon the beach]. Iliad xvii. 265.Iliad xvii. 265.