When the wave breaks on the shore it operates in the following manner: First, the overturning of its crest sends a great mass of water, it may be from the height of ten or more feet, down upon the shore. Thus falling water has not only the force due to its drop from the summit of the wave, but it has a share of the impulse due to the velocity with which the surge moved against the shore. It acts, in a word, like a hammer swung down by a strong arm, where the blow represents not only the force with which the weight would fall of itself, but the impelling power of the man's muscles. Any one who will expose his body to this blow of the surf will recognise how violent it is; he may, if the beach be pebbly, note how it drives the stones about; fragments the size of a man's head may be hurled by the stroke to the distance of twenty feet or more; those as large as the fist may be thrown clear beyond the limits of the wave. So vigorous is this stroke that the sound of it may sometimes be heard ten miles inland from the coast where it is delivered. Moving forward up the slope of a gently inclined beach, the fragments of the wave are likely to be of sufficient volume to permit them to regather into a secondary surge, which, like the first, though much smaller, again rises into a wall, forming another breaker. Under favourable conditions as many as four or five of these successive diminishing surf lines may be seen. The present writer has seen in certain cases as many as a dozen in the great procession, the lowest and innermost only a few inches high, the outer of all with a height of perhaps twenty feet. Along with the direct bearing action of the surf goes a to-and-fro movement, due to the rushing up and down of the water on the beach. This swashing affects not only the broken part of the waves, but all the water between the outer breaker and the shore. These swayings in the surf belt often swing the _debris_ on the inner margin over a range of a hundred feet or more, the movement taking place with great swiftness, affecting the pebbles to the depth of several inches, and grinding the bits together in a violent way. Listening to the turmoil of a storm, we can on a pebbly beach distinctly hear the sound of the downward stroke, a crashing tone, and the roar of the rolling stones.