Every wave takes them up and has fine fun with them. Pebbles and sand are picked up, swirled along, and thrown at the shore. They are sucked back as the wave is broken by the land. And then the following wave takes them, grinds them and scrubs them together. Thus they are jostled hither and thither, up and down the coast; and, as a result of the long, long fight, rocks and cliffs become pebbles, sand, or mud.

Now if you look at the pebbles on the shore you see that many of them are smooth and round. Some are as round as the "marbles" you play with. No wonder, for the mighty sea has scoured them with sand and rolled them for miles.

As you know, the sea is not always at the same height. It falls and rises. Twice in every day it ebbs and flows; we call this movement of the sea the tides. At low tide we can explore the very bed of the ocean. We can visit the homes of the living, breathing animals, which, at high tide, are hidden far under water. Between the high-water mark and low-water mark is our hunting-place. There we shall find the play-ground and feeding-ground of many a strange creature.

Here is a stretch of sand, with little channels of water; there is a patch of shingle mixed with numbers of tiny shells. The ebbing tide leaves shallow pools in every hollow of the beach, and these pools are often full of life.

Shrimps dart away and disappear in the sand as if by magic. Small fish and crabs hide from you as best they can. Helpless jelly-fish and starfish sprawl on the wet sand. What are those thin ropes of sand coiled up into little mounds? They remind us of "worm-casts." They are thrown up by a