If we consider this action alone, we cannot but recognize in it a cause sufficient to effect the removal of all the higher parts of the land to low levels, and eventually of all the low-lying land to the sea, in the course of such periods as geology makes us acquainted with. The mud-banks at the mouths of rivers show only a part of what rain and river action is doing, yet consider how enormous is the mass which is thus carried into the sea. It has been calculated that in a single week the Ganges alone carries away from the soil of India and delivers into the sea twice as much solid substance as is contained in the great pyramid of Egypt. “The Irrawaddy,” says Sir J. Herschel, “sweeps off from Burmah 62 cubit feet of earth in every second of time on an average, and there are 86,400 seconds in every day, and 365 days in every year; and so on for other rivers. Nor is there any reason to fear or hope that the rains will cease, and this destructive process come to an end. For though the quantity of water on the surface of the earth is probably undergoing a slow process of diminution, small portions of it year by year taking their place as waters under the earth,[44] yet these processes are far too slow to appreciably affect the supply of water till a far longer period has elapsed than that during which (in all probability) life can continue upon the earth. When we consider the force really represented by the downfall of rain, we need not greatly wonder that the levelling power of rain is so effective. The sun’s heat is the true agent in thus levelling the earth, and if we regard, as we justly may, the action of water, whether in the form of rain or river, or of sea-wave raised by wind or tide, as the chief levelling and therefore destructive force at work upon the earth, and the action of the earth’s vulcanian energies as the chief restorative agent, then we may fairly consider the contest as lying between the sun’s heat and the earth’s internal heat. There can be little question as to what would be the ultimate issue of the contest if land and sea and air all endured or were only so far modified as they were affected by these causes. Sun-heat would inevitably prevail in the long run over earth-heat. But we see from the condition of our moon how the withdrawal of water and air from the scene must diminish the sun’s power of levelling the irregularities of the earth’s surface. We say advisedly _diminish_, not _destroy_; for there can be no question that the solar heat alternating with the cold of the long lunar night is still at work levelling, however slowly, the moon’s surface; and the same will be the case with our earth when her oceans and atmosphere have disappeared by slow processes of absorption.