This is not all the story. What the sea takes away it gives again. Sir Thomas Holditch is our authority for saying that on some parts of the Pacific coast of America you may at some points see on the one hand dry land which by the shells found on it shows that the sea once flowed over it; while side by side with this raised land you may sail a boat over forests now sunk beneath the sea. The loss of bits and corners of England is serious--so serious that a Royal Commission on Sea Erosion, as the process is called, was appointed to inquire into the extent of the loss and the means by which it might be remedied. But in some parts of our coast the land is not losing, but gaining. If the sea takes away sand and gravel, chalk and shale and clay from the cliffs, these materials are not lost. Something is done with them. They must at some points, where the tides and currents of the sea deposit them, make the sea more shallow. Perhaps the sea lays them down as beds or sand-banks. Perhaps it carries them round the coast to some other point and there drops them. Can you not see that in this way the sea which at one point is dragging down the coast may at other points be building it up, or may be even constructing breakwaters made out of these stolen materials? The sea is not the only carrier which is thus laying down beds of material. The rivers are doing the same thing. Every shower of rain washes some dirt--by which we mean sand or gravel or loam or chalk--from the land into the nearest rivulet. The rivulet hurries with it down to the neighbouring river, and the river carries it down to the sea. If the river is going very fast it carries most of its dirt along with it, and we generally find the river muddy after rain. But when the river slackens its pace, as it usually does when it nears the sea and meets the sea's tides, then it lets the dirt fall; and thus at the river's mouth we find mud-banks or sand-banks. If a river is left long enough to its own devices, these sand-banks will so increase in bulk that the mouth of the river will become shallower and shallower and will spread. It silts up, and when a river is needed for the navigation of ships large sums of money have to be spent, as in the Scheldt or at the mouth of the Thames, in dredging this mud so as to keep the channels clear.