[Sidenote: Water and heat among the shaping forces of the earth.]
How the earth first came into being has not yet been clearly revealed. From the first, however, the mighty forces which act today, have shaped and fashioned the earth and prepared it for man's habitation. Water, entering the tiny cracks of the rocks, and expanding as, in winter, it changed to ice, crumbled the mighty mountans; water, falling as rain from the clouds, washed the rock fragments into the low-lying places to form soil; the water in mighty rivers chiseled the earth with irresistible force, as shown by the Grand Canyon of the Colorado. The internal heat of the earth, aided by the translocation of material by water, produced large cracks in the earth's crust, through which oceans of molten matter flowed and spread themselves over the land; the same heat appeared in volcanoes, through which were spurted liquid earth, cinders and foul gases; as the earth heat was lost, the crust cooled, contracted and great folds appeared, recognized as mountains, and as time went on, many of the mountains were caused to sink and the ocean beds were brought up in their stead. Wonderful and mighty have been the changes on the earth's surface since the Lord began its preparation for the race of men.
[Sidenote: The geological history of the earth is in many chapters.]
In the beginning, it appears that water covered the whole earth. In that day, the living creatures of earth dwelt in the water, and it was the great age of fishes and other aquatic animals. Soon the first land lifted itself timidly above the surface of the ocean, and formed inviting places for land animals and plants. Upon the land came, first, according to the story of the rocks, a class of animals known as amphibians, like frogs, that could live both in water and on land. Associated with these creatures were vast forests of low orders of plants, that cleared the atmosphere of noxious gases, and made it fit for higher forms of life. Then followed an age in which the predominating animals were gigantic reptiles, a step higher than the amphibians, but a step lower than the class of Mammals to which man belongs. During the age of these prehistoric monsters, the earth was yet more fully prepared for higher life. Following the age of reptiles, came the age of mammals, which still persists, though, since the coming of man upon the earth, the geological age has been known as the age of man.