Page:General History of Europe 1921.djvu/788

590 General History of Europe which has been carried on during the past hundred years with ever-increasing ardor and success, in both Europe and America. 1073. Great Age of the Earth. To begin with, almost every- one in Europe believed a hundred years ago that the earth had been created along with the sun, moon, and stars, and all the ani- mals and plants some five thousand years before. Modern geolo- gists, on the other hand, now believe that it must have required a hundred million, perhaps even a billion, years for the so-called sedimentary rocks to be laid down in the beds of ancient seas and oceans. Many of these rocks contain fossils, which indicate that plants and animals have existed on the earth from very remote periods. Accordingly it seems possible that for at least a hun- dred million years the earth has had its seas and its dry land, differing little in temperature from the green globe familiar to us. Even if we reduce this period by one half, it is impossible to form more than a faint idea of the time during which plants and the lower forms of animals have probably existed on the earth. Let us imagine a record's having been kept during the past fifty million years, in which but a single page should be devoted to the chief changes occurring during each successive five thousand years. This mighty journal would now amount to ten volumes of a thousand pages each ; and scarcely more than the last page (Vol. X, p. 1000) would be assigned to the whole recorded history of the world from the earliest Egyptian and Assyrian inscriptions to the present day. 1074. Lyell's Work in Geology. As early as 1795 the Scotch geologist James Hutton published his conclusion that the earth had gradually assumed its present form by slow natural processes. In 1830 Sir Charles Lyell published his famous Principles of Geology, in which he explained at great length the manner in which the gradual contraction of the globe and the action of rain and frost, had, through countless aeons, and without any great gen- eral convulsions or cataclysms, formed the mountains and valleys and laid down the strata of limestone, clay, and sandstone. He showed, in short, that the surface of the earth was the result of familiar causes, most of which can still be seen in operation,