Long, long ago, the rivers, the streams, the ocean, were at work, as they are now, carrying away rock and gravel, sand and earth. Then, as now, all this material, borne upon the rivers, washed to and fro by the ocean, settled down at the mouths of rivers or at the bottom of the sea, into a sediment, one layer forming over another, gradually built up through long ages. At first it was only a soft, loose, sandy or muddy sediment, such as you may see on the seashore, or in a mud-bank. But as the thickness of the sediment increased, the weight of the layers above gradually pressed the lower layers into firm hard rocks; and still, as the work of building went on, these layers were, in their turn, made solid by the increasing weight over them. Certain chemical changes had also a share in the transformation from soft mud to hard rock, which need not be here considered. All this has through thousands of years been going on. The land is perpetually crumbling away; and fresh land under the sea is being perpetually built up, from the very same materials which the sea and the rivers have so mercilessly stolen from continents and islands. This is the way, if geologists rightly judge, in which a very large part of the enormous formations of Stratified or Sedimentary Rocks have been made. [Illustration: VIEW IN A CANON.] So far is clear. But now we come to a difficulty. The Stratified Rocks, of which a very large part of the continents is made, appear to have been built up slowly, layer upon layer, out of the gravel, sand, and mud, washed away from the land and dropped on the shore of the ocean. [Illustration: SEA CLIFFS SHOWING A SERIES OF STRATIFIED ROCKS.] You may see these layers for yourself as you walk out into the country. Look at the first piece of bluff rock you come near, and observe the clear pencil-like markings of layer above layer--not often indeed lying _flat_, one over another, and this must be explained later, but however irregularly slanting, still plainly visible. You can examine these lines of stratification on the nearest cliff, the nearest quarry, the nearest bare headland, in your neighborhood. But how can this be? If all these stratified rocks are built on the floor of the ocean out of material taken _from_ the land, how can we by any possibility find such rocks _upon_ the land? In the beds of rivers we might indeed expect to see them, but surely nowhere else save under ocean waters. Yet find them we do. Through England, through the two great world-continents, they abound on every side. Thousands of miles in unbroken succession are composed of such rocks.