The temperature would now fall somewhat rapidly, and in a short space of time the surface of the earth would have become as cool as it is at the present day. Directly the waters of the firmament had collected into the oceans, leaving behind an atmosphere like that which now exists, geological agencies of the kind we are now familiar with would begin their sway. Air and rain would exert their insidious power upon the rocks, sapping their strength, converting the hardest granite into soft sand and clay, which would be washed away by the rain through brooks and rivulets into the channels of many rivers, all hastening with their burden of sediment, to deposit it finally in the sea. Here it would accumulate, layer after layer, building up those mighty masses of strata which now form the greater part of the visible land. While this general action was everywhere in progress, wearing down continents and islands towards the level of the sea, more specialised activities were assisting to the same end.
TWO STAGES IN THE LIFE OF THE EARTH
This illustrates in striking manner, based on the calculations of the best authorities, the comparative sizes of the earth, first as a gaseous mass, and, second, after it had cooled down and solidified into the planet on which we live. The small dot represents 8,000 miles, the earth’s diameter.
The waves which fall upon our coasts are now constantly undermining the cliffs and extending the margin of the sea at the expense of the land, and rivers not only serve to transport sediment, but cut down their channels deep into the rock, and so carve out the most varied landscapes of hill and valley from monotonous tableland.
Action of Winds and Tides
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.
THREE VIEWS OF THE GLOBE SHOWING HOW THE GREAT MOUNTAIN RANGES WERE FORMED