Thomas C. Chamberlin

“ Within the animal world, the preying of one form upon another is the main source of that great struggle for existence which has characterized the whole known history of life, and has been one of the influential factors in shaping the evolution of life and in modifying the special aspects assumed by the floras and faunas of each period. ”

“ That phase which treats of the outer relations of the earth is Cosmic or Astronomic geology; that which treats of the constituent parts of the earth and its material is Geognosy, of which the most important branch is Petrology, the science of rocks. That branch which investigates the structural arrangement of the material, or “the architecture of the earth,” is Geotectonic, or Structural geology; while that which deals with the surface changes and topographic forms, that is, with the face of the earth, is Physiographic geology. ”

“ It is so great that it can only be partially overcome by any force which human ingenuity can bring to bear upon it. This form of resistance has thus, not unnaturally, come to be regarded as approximately immeasurable, and perhaps as grading into actual immeasurability, and as resting back upon the actual contact of irreducible atoms. But the recent researches which have developed grounds for the conception that even the atoms are composite, lead to the further conception that their resistance to compression is dependent on the movement of their constituent corpuscles or electrons. ”

“ With the characteristics of river valleys and the methods by which they grow clearly in mind it is easy to say whether rivers have been the chief agents in the development of a given topography. River valleys are distinguished from other depressions on land surfaces by their linear form and, leaving out of consideration the relatively insignificant inequalities in a stream’s channel, by the fact that any point in the bottom of a river valley is lower than any other point farther up the stream in the same valley, and higher than any point farther down the stream. ”

“ The larger assemblages of life, which inhabit a continent or dwell in a great sea, are designated faunas and floras, as well as the smaller assemblages just discussed, but obviously in a broader and in a different sense. The disseverance of the land by the sea, or of the sea by the land, isolates the life and forces independent development. The introduction of cold zones, desert tracts, or other potent climatic belts has somewhat the same effect. So, measurably, does the raising of a mountain range or a plateau, or the sinking of critical portions of the sea-bottom. ”

“ Fossils as means of correlation.—While stratigraphy was thus, in the earliest stages, the main reliance in determining the order of events, and biology was the chief gainer, in the end stratigraphy received ample compensation, if indeed it did not become the greater beneficiary; for at no known and accessible place is there a complete succession of sedimentary beds. There are great series here and there, but their connections with one another are more or less concealed by surface formations or water-bodies. ”

“ Gradational processes belong to two categories—those which level down, degradation, and those which level up, aggradation. The transportation of material from the land, whether by rain, rivers, glaciers, waves, or winds, is degradation and the deposition of material, whether on the land or in the sea, is aggradation. Degradation affects primarily the protuberances of the lithosphere, while aggradation affects primarily its depressions. ”

“ The preceding discussion, and the illustrations which accompany it, give some idea of the topography which characterizes an area in various stages of its erosion history. Whether the valleys are deep or shallow, and the intervening ridges high or low, depends on the original height of the land and its distance from the sea. The higher the land, and the nearer it is to the sea, the greater the relief developed by erosion. A plateau near the sea may become mountainous in the mature stage of its erosion history, while a plain in the same situation would only become hilly. ”

“ Not only are inequalities necessary to the existence of land, but these inequalities must be renewed from time to time, or the land area would soon, geologically speaking, be covered by the sea. The renewal has been made again and again in geological history by movements that have increased the inequalities in the surface of the lithosphere. With each such movement, apparently, the oceans have withdrawn more completely within the basins, and the continents have stood forth more broadly and relatively higher, until again worn down. ”

“ We easily fall into the habit of thinking of molten rock as we think of a molten metal, merely as a substance which has passed from the solid to the liquid condition because of high temperature. With the return of low temperature a molten metal returns to the solid state usually in the same molecular condition which it possessed before. The point of fusion and the point of solidification are the same and are rigidly fixed. If this were true of the constituents of a rock, a definite order for the solidification of the several minerals might be anticipated. ”

“ In regions where the mantle rock is the product of the decay of the solid rock beneath, and such regions constitute a large portion of the earth’s surface, the soil and subsoil represent the excess of weathering over transportation. Since most of the earth’s surface is covered with soil to a greater or less depth, it is clear that, on the whole, weathering keeps ahead of transportation. Again, it is clear that the loosening of rock by weathering greatly increases the erosion which a given amount of moving water can accomplish. ”

“ The distribution of marine life is influenced by many factors, chief among which are temperature and depth of water. Not only is life more abundant in the warmer parts of the ocean than in the colder, but the species inhabiting cold waters are different from those in warm, and few species range through great variations. Many forms of life are restricted to shallow water. Many more, especially those which do not live on the bottom, swim about freely without reference to the depth of the water beneath them, while relatively few are restricted to great depths. ”

“ The question whether the volcanic gases are a contribution to the atmosphere and hydrosphere is so important in its bearings on the whole history of the atmosphere as to merit additional consideration here. As already noted, if the volcanic gases arise from water and absorbed air that have previously passed down through the strata, there is no real contribution to the hydrosphere and atmosphere, but merely circulation. If the gases are chiefly derived from the deep interior, they are an important accession to the atmosphere and hydrosphere. ”

“ Long before the continent reached base-level the rate of degradation, so far as dependent on mechanical erosion, would become so slow that the time necessary to bring the continent to sea-level would be almost inconceivably prolonged. Furthermore, it is quite possible that the land is suffering, or is liable to suffer, uplift, relative or absolute. If the rate of rise were equal to the rate of degradation the average height of the continent would of course not be affected. ”

“ A river is therefore to be looked upon not as a single straightforward current, but as a multitude of currents, some rising from the bottom toward the top, some descending from top to bottom, some diverging from the center toward the sides, and some converging from the sides toward the center. ”

“ Competitive relations.—The assembling of plants and animals, with their prodigious possibilities of multiplication, brought competition, and with it a struggle for food which often became a struggle for existence, and out of this grew innumerable modifications of form and habit. ”

“ While a glacier in a sense flows over a surface, it often cuts long, deep furrows in firm rock. It is difficult to explain this if the ice be so yielding as to flow under its own weight on a surface which is almost flat. If the mass is really viscous, its hold on its imbedded débris should also be viscous, and a bowlder in the bottom should be rotated in the yielding mass when its lower point catches on the rock beneath, instead of being firmly held while a deep groove is cut. ”

“ The history of the earth in the past has been intimately dependent upon that of the sun, and its future is locked up with the destiny of that great luminary. Geology in its broadest phases can therefore scarcely be separated from the study of the sun, but this falls within the function of the astronomer rather than the geologist. ”

“ The oblateness of the present earth is accommodated to its present rate of rotation. It is assumed that such accommodation has always obtained, and that if the rotation has changed, the form of the earth has changed also. Now, the more oblate the spheroid, the larger its surface shell and the less the total force of gravity. Hence if the earth’s rotation has diminished, its crust must have shrunk, because the form of the spheroid has become more compact, and the increase of gravity has increased its density. ”

“ The atmosphere blankets the earth and equalizes its temperature. Acting as a screen, it subdues in some measure the intensity of the sun’s rays by day, while it retards the radiation of the earth’s acquired heat at night. This is in some measure the function of all the constituents of the atmosphere, but by no means of all equally. The oxygen and nitrogen are relatively diathermous, letting the sun’s rays pass in freely, and the earth’s rays pass out freely ”

“ A stream is said to be loaded when it has all the sediment it can carry; it is loaded with fine material when it has all the fine material it can carry, and with coarse material when it has all the coarse it can transport. A stream loaded with coarse material flows more swiftly than one loaded with fine, for a larger percentage of a stream’s energy can be utilized in carrying fine material than coarse, and hence a larger percentage of the energy of a stream which carries a load of the latter will express itself in velocity. ”

“ For all general purposes, the limiting depth of living carbon-compounding plants may be set at 100 fathoms, as a generous figure—about the average depth of the border of the continental shelf—while the vast majority flourish only in the upper third of this depth.
Life does not cease here, for the products of this surface-life sink to greater depths and are fed upon by forms of sea animals that have become adapted to the dark and cold abyss of the ocean. Obviously, these deep-sea forms are a very distinct type of life, and constitute a fauna of the most pronounced kind, the abysmal fauna. ”

“ Metamorphism by heat and lateral pressure.—As already indicated, the more common intense pressures experienced by rocks at and near the surface are those that come from lateral thrusts arising from the shrinkage of the earth. These affect one dimension of the rock-mass, while they permit it to expand in one or both of the other dimensions. This produces a strain in all the constituent particles of the rock, and under such strain they pass more readily into solution than when free from strain, and more readily rearrange their molecules internally into positions of less strain. ”

“ Getting load.—If the surface on which the snow-field which is to become a glacier accumulates be rough and covered with abundant rock débris, as such surfaces usually are, the glacier already has a basal load when its movement begins, for the snow covers, surrounds, and includes such loose blocks of rock as project above the general surface and envelops all projecting points of rock within its field. When the snow becomes ice and the ice begins to move, it carries forward the loose rock already imbedded in it, and tears off the weak points of the enveloped rock-projections. ”

“ There is hardly a slope without loose material, and there is hardly an acre of low land below a slope on which running water has not deposited sediment washed down from above. When it is remembered that this is as true of gentle slopes and their surroundings as of steep slopes, though perhaps not to the same extent, and that a very large part of the earth’s surface is made up of sensible slopes, or of flats at their bases, some idea of the aggregate effect may be gained. ”

“ Most of the relics of life found in the stratified rocks belonged to animals or plants which lived in salt water. Because of their structure, their composition, their distinctive markings, and the remains of life which they contain, it is confidently inferred that most of the stratified rocks which lie beneath the mantle rock of the land were originally laid down in beds beneath the sea, and that the familiar processes of the present time furnish the key to their history. ”

“ The mechanical work of the rain.—In falling the rain washes the atmosphere, taking from it much of the dust, spores, etc., which the winds have lifted from the surface of the dry land. Not only this, but in passing through the atmosphere the water dissolves some of its gases, and perhaps particles of soluble solid matter. When therefore the falling water reaches the surface of the land it is no longer pure, and some of the gases it has taken up in its descent enable it to dissolve various mineral matters on which pure water has little effect. ”

“ The snow-field of a cliff glacier is sometimes no more than a great snowdrift, accumulated through successive years. Cliff glaciers are often as wide as long, and are always small, and between them and valley glaciers there are all gradations (Fig. 235) . Occasionally the end of a valley glacier, or the edge of an ice-sheet reaches a precipitous cliff, and the end or edge of the ice breaks off and accumulates like talus below. The ice fragments may then again become a coherent mass by regelation, and the whole may resume motion. Such a glacier is called a reconstructed glacier. ”

“ As the beds of sediment which it lays down follow one another in orderly succession, each later one lying above each earlier one, they form a time record. And as relics of the life of each age become more or less imbedded in these sediments, they furnish the means of following the history of life from age to age. The historical record of geology is therefore very largely dependent upon the fact that the waters have thus buried in systematic order the successive life of the ages. ”

“ The growth and constitution of a glacier.—The origin and history of a glacier is little more than the origin and aggregate history of the crystals that compose it. The fundamental conception of a glacier is therefore best obtained by tracing the growth of its constituent crystals. A basal fact ever to be kept in mind is that water in the solid form is always controlled by crystalline forces. ”

“ The alternative view that life developed primarily on the land and in the land-waters and migrated to the sea is not, however, without its support in the plant world, as we thus see, and the plant world was the primitive one; the dependent animal world necessarily followed its development. The hypothesis of a terrestrial origin of life throws a very suggestive cross-light on many geological problems, as will be seen later, and it may well be entertained as an alternative working hypothesis until the facts are more fully developed. ”

“ For the most part, the deposits of mud, sand, and gravel are made under the sea or in lakes and estuaries, but they are also formed on the land in lodgment basins, in low-gradient valleys, and on base-plains. The deposits of sediment on land have received less recognition than they deserve. When formed under the sea or in other life-sustaining waters, shells and other organic material are liable to be entrapped and to form a part of the rock. These organic remains, or fossils, greatly aid in interpreting the deposits in which they occur. ”