The wear of the sea is but little seen in such places as this, and still less so where the coast is low and flat, and the shore is very extensive and the water is shallow for a long distance. In fact, on many of these flat shores, instead of erosion taking place, the sea is adding to the land by depositing. This is particularly the case at the entrance of great, and of many small rivers. Their mud collects in the shallows at their mouths, and is added to by sand and shingle, so that land grows seaward, instead of the reverse. The seashore is then, usually, uninviting and often consists of large mud flats. Again, in some localities, where much sand collects on the surface of the rock forming the seashore, it may be “quick” in many places. The rising tide gets under the sand, which suddenly becomes like so much sand and water, and the falling tide leaves it hard for a while. The ordinary condition of a sandy shore is either that of a number of very slightly rounded stretches of sand, with drainage-streams between them, or it is pretty hard, readily dug into, and marked on the surface by ripples. The ripple-mark on sand always strikes the observer; it represents little ripple-like waves, wonderfully regular, and each has a ridge and a valley. They are very lasting, but disappear on the slightest movement of the wet sand as the tide comes in. These little ridges and valleys are not found when the water covers the sand at a considerable depth, but they are especially seen between high and low spring-tide limit. Such marks can be made, artificially, with sand, for instance, on the bottom of a large basin. If some sand is placed on the bottom, and water be poured in, and the edge of the basin be pushed, a to-and-fro movement of the water will occur, and it will be continued down to the sand. As the motion ceases, the sand will be seen to collect in ridges, side by side, and they will be perfect when the motion stops. Motion of the sea-water in one direction over soft sand will not produce ripple-mark well, but a slight to-and-fro movement will do it to perfection. Infinitely more wonderful than these ripples are the pebble beaches, for they often extend for many miles, and have a very considerable thickness. Worn, in the first instance, from distant rocks, born of huge bowlders, which the mighty waves laden with rolling stones have broken down, the pebble is formed by rolling against others, and the result of its wear and tear is carried off in the form of sand. They travel miles and miles along the coast with the tide, and therefore it is very common to find one kind of rock forming the coast-line, and the shore close by having pebbles made up of stone which is not known to be near at hand. Thus, on the coast of South Devon, the red rocks form the coast-line; they are sandy, and are covered in some places by a beautiful green vegetation. The sea is often of the brightest blue, or gray, when the sky is not much tinted with color.