When we enter into calculations we are astonished at the rapidity with which these agents perform their work even at the present day; but as we proceed farther back into the past, when the earth was full of youthful energy, their power must have been greatly enhanced. We might almost take the measure of the day as the measure of their work, for they probably accomplished as much during the eight hours’ day which once existed as they do now in twenty-four hours. A little consideration will make this clear. It is the winds which, blowing over the surface of the ocean, produce the sea waves, and it is these falling on our coasts that perform the work of marine denudation. But the winds are due in the first place to the heat of the sun, and the difference of temperature established at the equator and the poles; and, in the next place, to the rotation of the earth. Thus, with the increased rapidity of rotation which we know to have existed, and with increased radiation from the sun, a very probable contingency, the winds would increase in strength and more powerfully erode our coasts. Again, with the moon in greater proximity, and with a more rapid rotation of the earth, the tides would be much higher and more frequent, and these, raising and lowering the cutting edge of the sea, greatly assist it in its work of destruction. The winds and the tides produce various marine currents, and these help to distribute the sediment which the rivers deliver into the sea, so that when stronger currents flowed as a result of more powerful tides and more violent winds, the sediments would be strewn over wider areas; hence, the more ancient strata of our planet are far more widely distributed than are those of later time. [Illustration: THREE VIEWS OF THE GLOBE SHOWING HOW THE GREAT MOUNTAIN RANGES WERE FORMED In the days when the earth’s crust had formed but was still unstable, the process of cooling not having gone far enough, there would not be the mountains which now characterise it. These came when the earth contracted and crumpled up along certain well defined lines, which are now represented by the three great mountain chains of the world. ] [Sidenote: Building Up the Earth] Finally, a heavier rainfall would result from a more active atmospheric circulation, creating larger rivers, and thus, at the beginning, all those denuding agents which are engaged in wearing the land down into the sea would be working at a more rapid pace. Correspondingly, all the agents which are occupied in building up deposits of sediments would have extended their operations over a wider area, laying down a foundation broad and deep.