Where Do All the Little Round Stones Come From?
The little round stones you are thinking of are really pebbles which have been worn smooth and round by being rubbed against each other in the water, through the action of the waves on a beach, or the running water of brooks and streams. This sort of rock is called a water-formed rock. Some of them have travelled many miles before they are found side by side on the shore or in a large mass of what we would call conglomerate rock. But whenever you see a round smooth rock or pebble you may be quite sure that it was made round and smooth by the action of water.
You sometimes see large rocks made of small stones of various colors and sizes. You can often find a large rock of this kind standing by itself. If you examine it carefully, you will find it consists of an immense number of small stones of different sizes and of a variety of colors, all fastened together as though with cement. This kind of rock is called conglomerate. We know two kinds of conglomerate rock, one, quite common, in which the little stones are round and smooth, and another, not seen so often, in which the stones are sharp. The latter sort is sometimes called breccia, to distinguish it from the former, which is called true pudding stone.