Earth's surface

“ The answer seems to be this:—We have learnt by indirect methods that the Earth is a sphere; we have formed models approximately representing its shape and the distribution of its parts; generally when the Earth is referred to, we either think of an indefinitely extended mass beneath our feet, or else, leaving out the actual Earth, we think of a body like a terrestrial globe; but when we seek to imagine the Earth as it really is, we join these two ideas as well as we can—such perception as our eyes give us of the Earth’s surface we couple with the conception of a sphere. ”

“ Before we proceed to study detailed problems, then, it is obviously necessary to look at some general points connected with the relief of the earth’s surface and its causes.
In the words of the physical geographer, [20] the earth’s surface consists of the solid crust, or lithosphere, of the mass of water forming the seas and oceans and constituting the hydrosphere, and of that envelope of gas which we call the atmosphere. Considered separately, each of these is the concern of special sciences, and not of the geographer proper. ”

“ The area of the whole surface of the earth, land and sea, is less than 200,000,000 square miles, so that if the crust of the earth had been peeled off like the skin of an orange, spread out flat and plastered against the sun, it would have looked like a mere outlying patch beside the great congeries of sun-chasms constituting this gigantic spot. ”

“ 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 ”

“ Let us imagine the temperature of that liquid to be multiplied seven-fold, and then we shall obtain some conception of the fearful intensity of the heat which would be found in that wonderful celestial furnace the great sun in the heavens.
Ponder also upon the stupendous size of that orb, which glows at every point of its surface with the astonishing fervour that this illustration suggests. The earth on which we stand is a mighty globe; yet what are the dimensions of our earth in comparison with those of the sun? ”

“ It has been seen that igneous and aqueous agents have remodeled, from time to time, the physical geography of the globe. Can it admit of a doubt that changes in the physical structure of the earth’s surface will be accompanied with other changes in the organic productions of extensive areas? ”

“ In considering alterations of this kind, brought about in the physical geography of particular tracts, we are too apt to think exclusively of that part of the earth's surface which has emerged from beneath the waters, and with which alone, as terrestrial beings, we are familiar. ”

“ The material portion of the earth is altogether a surface film, an insignificant skin over the sphere of purity, the center of gravitation. Although men naturally imagine that the density and stability of the earth is dependent on the earthy particles, of which his own body is a part, such is not the case. Earth, as man upon the outer surface, can now know it, is an aggregation of material particles, a shell resting on this globular sphere of medial force, which attracts solid matter from both the outer and inner surfaces of earth, forming thereby the middle of the three concentric spheres. ”

“ We have but to consider the surface of this earth as having been upon a higher level; as having been every where the beds of rivers, which had moved the matter of strata and fragments of rocks, now no more existing; and as thus disposed upon different planes, which are, like the haughs of rivers, changing in a continual succession, but changing upon a scale too slow to be perceived. ”

“ On the Earth we find animated existence confined to the surface of the crust of the globe, to the lower and denser strata of the atmosphere, and to the film of water that constitutes the oceans. It does not exist in the heart of the rocks forming the body of the planet nor in the void of space surrounding it outside the atmosphere. ”

“ If the Earth were a globe, it is evident that everywhere the water of its surface, the seas, lakes, oceans, and rivers, must be sustained the land, the Earth must be under the water; but if the land and the waters are distinct, and the Earth is “founded upon the seas,” then everywhere the sea must sustain the land as it does a ship or any other floating mass, and there is water below the earth. ”

“ It has been asked whether a study of the solar atmosphere may not throw some light upon the peculiar constitution of the upper strata of the earth's surface, which are known to be of less density than the average interior of our planet. ”

“ But though every operation of the globe be necessarily required for the explanation of those appearances which we now examine, it is principally the action of the sun and atmosphere, and the operations of the waters flooding the surface of the earth, that form the proper subject of the present investigation. ”

“ Thus all the surface of this earth is formed according to a regular system of heights and hollows, hills and valleys, rivulets and rivers, and these rivers return the waters of the atmosphere into the general mass, in like manner as the blood, returning to the heart, is conducted in the veins. ”

“ We now alight upon that solid mass, Earth, the most fixed and substantial of all{xiii} the elements. The surface of our planet is composed of dry land and water; of which the ocean, without including lakes and rivers, occupies by much the largest extent. ”

“ 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 no longer [18] possible for any one to believe with our forefathers that the earth’s surface has always existed as it now exists. For the science of geology has proved to demonstration that seas and lands are perpetually undergoing gradual changes of relative positions—continents and oceans supplanting each other in the course of ages, mountain-chains being slowly uplifted, again as slowly denuded, and so forth. ”

“ The earth receives its heat from the sun; a portion of it is conducted from particle to particle into the interior of the rocky crust. Another portion produces warmth in the atmosphere around us, by convection, or the circulation of particles; those warmed by contact with the surface becoming lighter, and ascending to give place to the colder and heavier ones. A third portion is radiated off into space, according to laws which have not been sufficiently investigated, but which are dependent upon the colour, chemical composition, and mechanical structure of the surface. ”

“ The earth is an irregular sphere, one of a number of planets circling the sun, from which we get light, heat and radiation. The earth has a shell or crust made of various minerals. Two-thirds of its surface is water of various depths up to six miles. Above the surface is an atmosphere, some twenty miles thick, composed of various gases, dust particles and water vapor. Operating throughout the earth there are vibrations of different wave lengths. ”

“ Much earth remained upon the rock, in irregular masses, but the woods had been felled, and the water had free access to the surface, and to the crevices which sun and frost had already produced in the rock, and, of course, to the slimy stratum beneath. ”

“ The material crust of the earth rests on this placid sphere of vigor, excepting in a few places, where, as in the crevice we have entered, gaps, or crevices, in matter exist, beginning from near the outer surface and extending diagonally through the medial and inner spheres into the intra-earth space beyond. This medial sphere is a form of pure force, a disturbance of motion, and although without weight it induces, or conserves, gravity. It is invisible to mortal eyes, and is frictionless, but really is the bone of the earth. ”

“ The geologists tell us that such natural forces have remodeled and recast the various areas of the earth and that they account for the present structure of its surface. These men of science and the astronomers and the physicists tell us that in some early age the world was not a solid globe, with continents and oceans on its surface, as now ”

“ We shall now proceed to find out what would be the internal form, and greatest density of the earth, under the supposition that it is a hollow sphere divided into two equal volumes and masses—exterior and interior—meeting at 817 miles from the surface; but before entering upon this subject we have something to say about the notion of the earth being solid to the centre. ”

“ The level of its surface, however, is varied by hills and mountains, which, though insignificant in comparison with the size of the whole earth, are enormous when compared with the structures of human hands. ”

“ Terrestrial globe on which the position of the principal places on the surface of the earth are shown according to the principal observations of the most celebrated astronomers and geographers of our times by the labor of John Gabriel Doppelmayr, mathematician, professor and publisher of Nürnberg. ”

“ The solid part of the earth is therefore composed of (1) a thin layer of unconsolidated or earthy material, a few feet to a few hundred feet in thickness, covering (2) a layer or zone many thousands of feet, and probably many miles, thick, composed of solid rock comparable to that exposed at numerous points on the surface, and (3) a central mass, to which the preceding layers are but a shell, composed of hot, dense, and rigid rock, the real nature of which is not known by observation. ”

“ 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. ”

“ The diversity of heights upon the surface of the earth, and of hardness and solidity in the masses of which the land is formed, is doubtless governed by causes proper to the mineral kingdom, and independent either of the atmosphere or sea ”

“ If we imagine an observer contemplating the earth from a « 58 » convenient distance in space, and scrutinizing its features as it rolls before him, we may suppose him to be struck with the fact that eleven-sixteenths of its surface are covered with water, and that the land is so unequally distributed that from one point of view he would see a hemisphere almost exclusively oceanic, while nearly the whole of the dry land is gathered in the opposite hemisphere. ”

“ Below this lay the sphere of 'air', below this again that of 'water', and lowest or in other words, most central of all was the sphere of 'earth', the solid foundation of the whole structure. Water might be said to be above earth because nowhere was there water to be found without earth beneath it, but the surface of water was always equidistant from the centre, whereas earth had prominences which rose above water. ”

“ To-day, the crust of the earth, that is, the entire surface of the lithosphere, is conceived as being constituted of earth columns, all of which rest with equal weight upon the level of complete compensation, which exists at a depth of some 76 miles below land surfaces. ”

“ What is this wide-spread component of the surface of the earth? and whence did it come?
You may think this no very hopeful inquiry. You may not unnaturally suppose that the attempt to solve such problems as these can lead to no result, save that of entangling the inquirer in vague speculations, incapable of refutation and of verification. If such were really the case, I should have selected some other subject than a "piece of chalk" for my discourse. ”

“ An envelope of air, termed the atmosphere, which surrounds the whole globe; (2) A lower and less extensive envelope of water, known as the hydrosphere (Gr. ὕδωρ, water) which, constituting the oceans and seas, covers nearly three-fourths of the underlying solid surface of the planet; (3) A globe, called the lithosphere (Gr. λίθος, stone) , the external part of which, consisting of solid stone, forms the crust, while underneath, and forming the vast mass of the interior, lies the nucleus, regarding the true constitution of which we are still ignorant. ”

“ Without dust there would be no blue firmament. The sky would be as dark as or darker than we see it in the finest moonless nights. The glowing disk of the sun would stand immediately upon this dark background, and the same sharp contrast would prevail upon the illuminated surface of the earth—blinding light, where the sun's rays fall, and deep black shadows where they do not. ”

“ By laws, the origin of which we have not yet traced, the condition of the diffused heat was changed, and the particles of the gaseous matter, condensed and agglomerated by attraction, into a series of planets, of which our earth is the third in point of size. That the earth has undergone vast changes, is evident to the most superficial geological student. ”