Page:Popular Science Monthly Volume 33.djvu/835

Rh well to remember that great though the changes in human affairs have been since the most remote epochs of which there are records in monument or history, nothing indicates that within this period there has occurred any appreciable modification of the main outlines of land and sea, or of the conditions of climate, or of the general characters of living creatures. The distance that separates us from those days is as nothing when compared to the remoteness of past geological ages. No numerical estimate on which reliance can be placed has yet been made of the duration even of that portion of geological time which is nearest to us; and we can say no more than that the earth's past history, as recorded in what we now find upon it, or as inferred from what we find, probably extends over hundreds of thousands or millions of years. It is through the facts of geography, as now acquired and interpreted, that the geologist is supplied with the means of arriving at the true signification of much that occurred in past time, the traces of which survive in physical features or organic forms. He finds that the most important agencies in determining and modifying the present conditions of existence on the earth, whether as affecting inorganic nature or organic beings, are closely connected with the actual distribution of land and sea, and the configuration of the surface; and he learns that it is through these agencies that he must seek to unravel the intricacies of the past.

The study of geology, in its turn, enables the geographer to understand many things that would otherwise be unintelligible to him. He thus learns how the boundaries of sea and land have been determined; where connections formerly existing have been severed; how islands have risen from the ocean and may be sinking below it; to what causes are due the rocky coasts and headlands, the indentations of the coasts, the formation of bays and fiords; at what time and by what means mountains have been raised up, plains laid out, valleys excavated, and the courses of rivers and positions of lakes fixed; and he is taught the constituents and qualities of the materials forming the surface of the earth, of the soil upon it, and of the minerals beneath it. And as a better insight is obtained into the natural relations of the mountains, the plains, the valleys, rivers, lakes, and seas, the conviction arises that the ever-diversified details of the face of the globe are in no sense accidents or fortuitous results, little worthy, as such, of admiration unless for their picturesque forms or wonderful proportions; but that they are the direct, orderly, and necessary outcome of the action of forces simple in themselves, and operating in accordance with well-known and invariable physical and mechanical laws. The perception of general characteristics of structure among the various features of the earth's surface that pass