Lithosphere

“ In the stricter sense, physical geography is that part of geography which involves the processes of contemporary change in the crust and the circulation of the fluid envelopes. It thus draws upon physics for the explanation of the phenomena with the space-relations of which it is specially concerned. Physical geography naturally falls into three divisions, dealing respectively with the surface of the lithosphere—geomorphology ”

“ Wrong impressions concerning the figure of the lithosphere are sometimes gained because its depressions are obliterated by the oceans. The oceans are, indeed, useful to us in showing where the depressions are located, but the figure of the earth which we [11] are considering is the naked surface of the rock. In a broad way, the earth’s shape will be given by the arrangement of the oceans and the continents. As soon as we take up the study of this arrangement, we find that quite significant facts of distribution are disclosed.
Fig. ”

“ All the tectonic movements of the solid nucleus produce changes in the mobile lithosphere. Volcanic and seismic activity is manifested, mountains are folded, levels change, fresh surfaces are exposed to denudation, erosion and deposition. ”

“ We may thus speak of the great world-ridges as regions of dominant elevation, and of the profound oceanic troughs as areas of more or less persistent depression. From one point of view, it is true, no part of the earth’s surface can be looked upon as a region of dominant elevation. Our globe is a cooling and contracting body, and depression must always be the prevailing movement of the lithosphere. The elevation of the continental plateau is thus only relative. ”

“ To us north and south, east and west are of equal interest and importance. Our desire now is to understand, if haply we may, the complex system of which we ourselves form a part. The distribution of land and water—the configuration of continental areas and oceanic basins—the circulation of oceanic and terrestrial waters—earth-movements and volcanoes—ice-formations—the atmosphere—climatology—the geographical distribution of plants and animals—in a word, the world as one organic whole now forms the subject of our contemplation. ”

“ Every change tended to let the earth draw in its (imaginary) belt, a notch at a time. The forces of contraction acted along the line of the equator, and formed folds running toward the poles. In this early time the great mountain systems were born, and they grew in size gradually, from small beginnings.
These mountains of upheaval, made by the bending of the earth's crust, and the formation of alternating ridges and depressed valleys, are many. The [Pg 128] earth is old and much wrinkled. Other mountains have been formed by forces quite different. ”

“ It is doubtful if such an earth would be suitable for life,—certainly not for man.
The Real Earth of Land, Water, and Inclined Axis. The different manner in which land and water surfaces absorb, radiate, and reflect the heat from the sun has a profound influence on climate, which also is modified by latitude, elevation above sea level, elevation above a valley or above a surrounding plane, direction of wind, height and trend of direction of hills and mountains, the position of lakes and inland seas, the relative position and magnitude of continents and oceans, storm tracks, and ocean currents. ”

“ But the skin of the earth is restless, as the inner fires waver in their long cooling. Beneath the volatile cloak of air, and the tidal robe of waters, the rocky layer encrusting the unknown vast core of the earth moves in its own hour. A slow adjustment, a period of planetary shudders, and a land is engulfed, a continent pressed upward. ”

“ The patient study of the rocks has revealed the origin of the present configuration of the land. There is not a hill or valley, not a plateau or mountain-region, which does not reveal its own history. The geologist can tell you why continents are bordered by coast-ranges, and why their interiors are generally comparatively low and basin-shaped. The oceanic basins and continental areas, we learn, are primeval wrinkles in the earth’s crust, caused by its irregular subsidence upon the gradually cooling and contracting nucleus. ”

“ Yet again, geologists teach us that the Earth's surface has been growing more varied in elevation—that the most ancient mountain systems are the smallest, and the Andes and Himalayas the most modern; while in all probability there have been corresponding changes in the bed of the ocean. As a consequence of these ceaseless differentiations, we now find that no considerable portion of the Earth's exposed surface is like any other portion, either in contour, in geologic structure, or in chemical composition ”

“ Every rock beneath our feet has its story of change to tell us. Mountains, valleys, and plains, continents and islands, have passed through vicissitudes innumerable, and bear within them the evidence of a gradual development or evolution. Looking back through the vista of the past one sees the dry lands gradually separating from the ocean, and gathering together into continental masses according to a definite plan. It is this slow growth, this august evolution, carried on through countless æons, which most impresses the student of physical geology. ”

“ The cause of this change of level in the water-surface is the attraction exerted by the sun and moon upon the ocean. The earth is, so to speak, clothed with a flexible garment of water, and this garment is pulled out of shape by the attractive force of our luminaries; very roughly speaking, we may say that the ocean-surface is distorted into a shape called an ellipsoid, and that there are therefore two elevations of water which march across the sea-covered regions of the earth as it revolves on its axis. ”

“ When a polar continent heaves from the bosom of the deep, or when the inquiring eye rests upon the serrated rock, the antique victim of some drift-dispersing glacier, the mind perceives the effects and recognizes the existence of nature's omnipotent muscles, and their appalling power. ”

“ Here the science of geology takes its start with the metamorphic rocks, and it is the dividing line between the inner, smaller, and the outer, larger, planets.
IV. The Terraqueous Stage, when the surface has become substantially stable, there are great oceans gradually diminishing in size, and land gradually increasing. This is the stage of the sedimentary rocks, the time when the planet passes from its own supply of heat to dependence upon that of the sun; the stage when life begins, and the one in which the Earth is now. ”

“ It is a vast ocean of underground water, with mountains of water and valleys of water.
A great lake marks an underground soakage water level. A riverbed marks an underground seepage topography. The sea of water inside a continent is just as much a map of hills and dales of water as the land is a map of the hills and valleys of geography. The water is dynamic, it is flowing. The land surface is dynamic and rain fed; it is creeping soils. ”

“ We know by ordinary experience that the earth is composed of rock, sand, soil, etc., and generally covered, where there is no running or standing water in the form of rivers, lakes, or seas, with vegetation, such as trees and grass. Further experience teaches us that the earth is very large, and that its surface is divided into wide areas of land and of water. The largest bodies of water, the oceans, taken all together, cover about 72 per cent., or nearly three-quarters of the entire surface of the earth. ”

“ Now, it is a fact of which the very first principles of geology assure us, that the solids of the globe cannot for a moment be exposed to water, or to the atmosphere, without becoming liable to change. They instantly begin to wear down. ”

“ The globe is divided into five parts, termed zones, and all that portion is subject to severe cold and perpetual frost, which is under the two extremities, about each of the poles, the nearer of which is called the north, and the opposite the south, pole. The middle of the earth, over which is the orbit of the sun, is parched and burned by the flame, and is consumed by being so near the heat. ”

“ If the solid substance of the earth formed a perfect sphere in ante-geologic times—that is, in ages preceding those to which our present geologic studies extend—there can be no doubt that there was then no visible land above the surface of the water; the ocean must have formed a uniformly deep covering to the submerged surface of the solid globe. In this state of things, nothing but the earth’s subterranean forces could tend to the production of continents and islands. ”

“ HOW THE MOUNTAINS WERE UPHEAVED. The notion that the ground is naturally steadfast is an error,—an error which arises from the incapacity of our senses to appreciate any but the most palpable, and at the same time most exceptional, of its movements. The idea of terra firma belongs with the ancient belief that the earth was the centre of the universe. It is, indeed, by their mobility that the continents survive the increasing assaults of the ocean waves, and the continuous down-wearing which the rivers and glaciers bring about.—Professor Shaler. ”

“ Numerous inscriptions relate to well-known geographical discoveries. Meridian and parallel circles are drawn on the globe at intervals of five degrees, the principal ones, including the equator, the tropics, and polar circles, being made especially prominent. ”

“ Geologists who believe that mountain-chains have been thrown up suddenly 156 at many successive epochs, imagine that the waters of the ocean may be raised by these convulsions, and then break in terrific waves upon the land, sweeping over whole continents, hollowing out valleys, and transporting sand, gravel, and erratics, to great distances. ”

“ Tilted and convoluted, broken and crushed by myriad earth-movements—scarred, furrowed, worn and degraded by — 348 — the frosts, the rains, the rivers, and the seas of countless ages—the rocks of our Continent are yet eloquent of design. Where the ignorant sees nothing save confusion and discord, the thoughtful student beholds everywhere the evidence of a well-ordered evolution. ”

“ Simply by that science of the geographer which demonstrates that the earth is not flat, but spherical, and that the heavens have not edges, like a skin-tent or glass-case, to come anywhere in contact with it, but consist mainly of a diffused atmosphere, with illimitable space beyond. ”

“ If we can picture to ourselves the formation in those remote ages, that it is the geologist’s task to rehabilitate in thought, of a vast ridge, not sharp like the typical mountain range, but of broad dimensions like the swell of some vast ocean, we shall have the material then forming [4] the earth’s crust bent upwards, and in unelastic places broken, and this partly or entirely beneath the ocean. ”

“ As the earth is a globe, and as all its vast collections of water—its oceans, lakes, &c., are sustained by the earthy crust beneath them, and as beneath this ‘crust of the earth’ everything is in a red-hot molten condition to what place could the excess of waters retire which are said in the scriptures to have overwhelmed the whole world? ”

“ Finally, physical geography is permitted to spread over much the same ground from a natural-science standpoint, giving many additional and interesting facts and laws concerning zones, volcanoes, ocean-beds and currents, atmospheric phenomena, geologic history, etc. The same earth, the same lands and oceans, furnish the outline in each case, and we travel over the same ground three or four times successively, each time adding new facts to the original nucleus. ”

“ Large plains and variously indented continents are raised or sunk, lands are separated from seas, and the ocean itself, which is permeated by hot and cold currents, coagulates at both poles, converting water into dense masses of rock, which are either stratified and fixed, or broken up into floating banks. ”

“ The dislocation of the crust of the globe elevated the mountains, dug the valleys, sank the seas, formed the continents, and, toward the end of the Tertiary period, the globe presented a surface much resembling what we see now. ”

“ Know that the earth has the form of a globe suspended in the centre of the heavens. It is divided by the two great circles of the meridian and equator, which cut each other at light angles, into four equal parts, namely, those of the north-west, north-east, south-west, and south-east. The inhabited portion of the earth is situated in the southern hemisphere, of which one half is inhabited. ”

“ Thus we draw the important inference that if, the oceans having been removed, we were then to remove from the earth’s surface a rind two miles thick—a thickness which, it is to be observed, is only the two-thousandth part of the earth’s radius—we should transform the earth into a globe which, while it still retained appreciably the same size, would have such a temperature that even the coolest spot would be as hot as boiling water. ”

“ In like manner, when the geologist surveys the convexity of his own globe, he finds its solid covering composed of rocks and beds of all shapes and kinds, lying at every possible angle, occupying every possible position, and all of them, generally speaking, at the same distance from the earth’s centre. Every where we see what was deep brought into visible relation with what was superficial—what is old with what is new—what preceded life with what followed it. ”

“ If we accept the glacial theory—a hypothesis pretty well established now among scientific men—we 79 may readily conceive that, as the sun melted the ice at a greater distance in both directions from the equator, the habitable area of the earth’s surface would gradually become enlarged. ”