You have heard, perhaps you have even seen, something of the destruction which is worked by the waves of the sea. Every year piers and sea walls are broken down, pieces of the coast are washed away, and the shores are strewn with the wreck of ships. So that, beside all the waste which the surface of the land undergoes from rain, and frost, and streams, there is another form of destruction going on along the coast-line. On some parts of the coast-line of the east of England, where the rock is easily worn away, the sea advances on the land at a rate of two or three feet every year. Towns and villages which existed a few centuries ago, have one by one disappeared, and their sites are now a long way out under the restless waters of the North Sea. On the west coast of Ireland and Scotland, however, where the rocks are usually hard and resisting, the rate of waste has been comparatively small. It would be worth your while the first time you happen to be at the coast, to ascertain what means the sea takes to waste the land. This you can easily do by watching what happens on a rocky beach. Get to some sandy or gravelly part of the beach, over which the waves are breaking, and keep your eye on the water when it runs back after a wave has burst. You see all the grains of gravel and sand hurrying down the slope with the water; and if the gravel happens to be coarse, it makes a harsh grating noise as its stones rub against each other—a noise sometimes loud enough to be heard miles away. As the next wave comes curling along, you will mark that the sand and gravel, after slackening their downward pace, are caught up by the bottom of the advancing wave and dragged up the beach again, only to be hurried down once more as the water retires to allow another wave to do the same work. By this continual up and down movement of the water, the sand and stones on the beach are kept grinding against each other, as in a mill. Consequently they are worn away. The stones become smaller, until they pass into mere sand, and the sand, growing finer, is swept away out to sea and laid down at the bottom.