Alfred Wegener

“ The adherents to the doctrine of the bridging-continents have up to the present made no differentiation between the bridges over the oceans and those over the continental shelves. It must be especially emphasized that the displacement theory only deals with the question of land connection over the present-day deep sea areas for which new ideas are developed, whilst for the shelf-bridges, as the Bering Straits between North America and Siberia, the earlier view of submergence and re-emergence of dry land remains absolutely undisputed. ”

“ If, on the other hand, we had not taken away from the observed values the influence of the masses above the sea-level, we should not have obtained such gravity anomalies in the region of the mountains, but—although with minor deviations—have found normal values there. Subterranean mass-defect and mass-excess above the sea-level therefore mutually counterbalance, isostasy thus prevailing in mountain masses. Since this is proved to be the same in ancient as well as recent mountains, we arrive at the principle: the folding of mountains is a compression subject to the preservation of isostasy. ”

“ Although the grounds for the shifting of the poles (in certain periods of the earth’s history) are so compelling, nevertheless it cannot be denied that all previous attempts to fix the positions of the poles continuously throughout the whole geological succession have always led to self-contradiction, and indeed to contradiction of so grotesque a kind that it is not to be wondered at that the suspicion arises that the assumption of a shifting of the poles is built upon a fallacy. ”

“ We will consider the grounds of both views in turn, beginning with those of viscosity. They are especially the phenomena of isostasy, the continental displacements, the movement of the poles, and the flattening of the earth near the poles.
It is a well-known fact that isostasy, the equilibrium of adjoining portions of the earth's crust, is universally satisfied on a large scale. Just as indubitable is the occurrence of vertical movements of compensation tending to the restoration of isostasy wherever it has been disturbed over a great area. ”

“ Whilst the continental blocks are wrinkled in all directions by ancient and recent folded mountain chains, we do not know, in spite of all the soundings that have been made, a single feature from the enormous area of deep sea which we could claim with any certainty as a chain of mountains. ”

“ A very sharp control on our supposition that the Atlantic is formed of an enormously expanded rift, the margins of which formerly directly adjoined each other, is exercised by a comparison of the geological structures on both sides; for it is to be expected that folds and other structures, formed before the separation, will be continuous from one side to the other, and their terminations on both sides of the ocean must lie exactly in such a position that they appear as immediate continuations in the reconstruction. ”

“ Just as a drying apple becomes wrinkled by folds on its surface through the evaporation from its interior, so should the earth through cooling and the consequent shrinkage form folded mountain chains on its surface. ”

“ It is important to observe that the evolution of the sial crust must be one-sided, even if the forces vary, for tension cannot smooth out the folds of a continental block, but at the most can only tear them to pieces. The alternating action of the forces of compression and tension is thus not able to undo its operations, but produces unilateral progressive results: crumpling and dismemberment. The covering of sial becomes continually smaller in area, and thicker, in the course of the earth’s history, but it also becomes increasingly split up. ”

“ Finally, in the Lower Carboniferous we find in Spitsbergen the tree-like Calamites, Lepidodendra, tree-ferns; in short, the same flora as that of the great coal-deposits of the Upper Carboniferous of Europe, which, in the judgment of those best qualified to form an opinion, was tropical. Therefore the climate of Spitsbergen must have been at that period about 30° C. higher than to-day.
This enormous variation of climate from a tropical to a polar one immediately suggests a displacement of the poles and of the equator, and therefore of the whole zonal system of climates. ”

“ The arguments of the opposing doctrine of the permanence of continents and oceans rest not on biological but on geophysical grounds, and are directed essentially not against the former existence of land connections, but only against that of bridging-continents. The first argument consists in the facts already touched on, that on the continents deep-sea deposits do not occur to any considerable extent, so that the continental blocks as such are undoubtedly “permanent.” ”

“ We must obviously here assume that the great compression of the Himalayas has exerted a pull on the ranges of Further India in the direction of their length, that under the influence of this pull the Sumatra range has been torn off at the northern end of the island, and that the northern portion of the chain (Arakan) has been drawn northwards like an end of a rope into the great compression, and is still being so drawn. Planes of differential movement must have been formed by this process on both sides of this enormous horizontal displacement. ”

“ Thus, according to our idea, the island festoons, especially those of Eastern Asia, are to be considered as marginal ranges, which, by the westerly drift of the continental masses, become separated from them, because those festoons remain attached to the deeply-solidified ancient floor of the sea. The younger and more mobile ocean floor crops out in a window-like fashion between them and the continental margin. ”

“ If we merely place the South Pole in the conceivably best position (50° S. 45° E.) in the midst of these traces of ice, the remotest traces of land-ice in Brazil, India and Eastern Australia would possess a geographical latitude of not quite 10°, that is, a complete hemisphere of the earth was buried beneath the ice, and had therefore also the polar climate necessary for that purpose. ”

“ But the most striking relations are shown by the numerous genera of Megascolecinæ, which connect Australia, and either the North Island of New Zealand, or the whole area of New Zealand, with Ceylon, and, in particular, Southern India, and sometimes also the north of India and of Further India (and, strange to say, occasionally the west coast of North America) . The fact that the earthworms show no relationship between Australia and Africa confirms our assumption that these continents did not directly adjoin one another, but were connected only through India and Antarctica respectively. ”

“ Even these purely biological facts show the distinct advantages which the displacement theory possesses over that of the submerged bridges. The distance from the nearest points of South America and Australia, namely, Tierra del Fuego and Tasmania, amounts to-day to 80°, measured along a great circle, that is, quite as much as that between Germany and Japan. Central Argentina lies just as far from Central Australia as from Alaska, or as South Africa from the North Pole. Does one really believe that a mere land connection is sufficient to secure the exchange of forms? ”

“ It is not inconceivable that the vulcanicity occurs so frequently near the coasts, because the inclusions of sima of the block are pressed out by the field of stress described above. This explanation is more especially possible in the case of oceanic islands which are surrounded in a circular manner by this field of stress.
A special kind of force must occur on the margin of the plastic continental blocks when these are loaded by a covering of land-ice. If one loads a plastic cake, it will, in its effort to reduce its thickness and extend horizontally, become affected by marginal cracks. ”

“ He thought that the festoons originated through a tensile force in the crust of the earth coming from the Pacific. The festoons of islands, together with a broad zone of the neighbouring mainland, also characterized by the curved course of the coast and of the elevations, would form a great system of fractures. The area between the chain of islands and the coast of the mainland would be the first continental step which would be submerged below the surface of the sea on the west, as a consequence of a tilting movement, whilst the eastern margin would project as an island-festoon. ”

“ Folding on the anterior margin of drifting blocks seems at first sight to offer difficulties in comprehension, since the sima should surely be the more liquid and the sial the more rigid material. But we must remember our comparison between sealing-wax and wax. Thus if the sial block can be considered as solid, like wax, it will nevertheless be folded when the forces of displacement exceed a certain value. The sima certainly gives way and flows as sealing-wax does—but an exceedingly long period of time is needed for that. ”

“ The huge masses of sial, which become depressed to great depths by the folds, must be melted there and spread out beneath the adjacent parts of the blocks, which therefore become elevated. If in this connection we confine ourselves to the highest region of the Asiatic block, lying on an average about 4000 m. above the level of the sea, measuring 1000 km. in the direction of thrust, and if, in spite of the much greater elevation, we take only a similar shortening to that of the Alps (namely, to a fourth of its original length) , we obtain a displacement of India of about 3000 km. ”

“ The basic principles are the same as for the similar phenomena which were illustrated for the interior of the continental blocks in Fig. 33 (p. 166) , but mentally transferred to the continental margin. If the block moves towards the sima, then marginal folding occurs, and may be accompanied either by overfolds or thrusts or by echeloned folds, according to the direction or the movement. If it moves from the deep-sea floor, then the coastal chains will split off. But if the movement is a shearing one, then we have a fault with lateral displacement, and the marginal chain slides longitudinally. ”

“ But why is it just those portions of the blocks that have especially thick sedimentary deposits which are later involved in the folding? Such regions with heavy sedimentation are known as geosynclinals (basins) . Haug formulated the law thus: mountain chains are formed from geosynclinals. [1] Probably it might be better expressed: from continental shelves; because a marginal shelf—as, for example, that from which the South American Andes are built—can hardly be called a basin. There are a variety of reasons why the shelves are favoured by folding. ”

“ Since steep vertical walls, of the height here in question, would make much too great demands on the resistance to pressure of the rocks, inclined gliding planes of slipping are formed simultaneously with the rift, or in place of it, along which the marginal parts of both portions of the block sink into the rift as it opens, to the accompaniment of numerous local earthquakes, so that only a rift-valley of moderate depth is exposed to view, with its floor formed of faulted blocks of the same series of rocks as those which occur in situ high up on the margin of the trough. ”

“ The most striking to the eye are the Carboniferous folds, which E. Suess calls the Armorican mountains, and which make the coal deposits of North America appear as the direct continuation of the European. These strongly planed-down chains, coming from the interior of the continent, stretch in Europe at first in a curved course towards the W.N.W., then westwards so as to form a wild jagged type of coast (the so-called rias-coast) in south-western Ireland and Brittany. ”

“ Eötvös was the first to claim that a force exists which endeavours to displace the continental blocks towards the equator. [3] He especially drew attention to the fact “that the direction of the vertical is curved in the plane of the meridian, the concave side turned to the pole, and that the centre of gravity of the floating body lies higher than that of the displaced mass of liquid. As a result, the floating body is subjected to the action of two forces working in different directions, the resultant of which is directed from the pole towards the equator. ”

“ We have also the circumstance of decisive importance that although the adjustment of the blocks must be made on the grounds of other phenomena, especially their outlines; yet by this adjustment the continuation of each structure on one side is brought into exact contact with the corresponding end on the other. It is just as if we put together the pieces of a torn newspaper by their ragged edges, and then ascertained if the lines of print ran evenly across. ”

“ When we bring into consideration horizontal drift movements of the continents, we can only uphold this principle so far as to agree that the total areas of the continental blocks and of the ocean floors, except for the compression of the former in the course of time, remain approximately constant. ”

“ This spreading out can only be symmetrical on both sides when the crust has no progressive movement over the sima. But if the crust is displaced—not taking into account its folding movements—as a whole over the sima (which will almost always be the case) , then the spreading out of the sial masses must take place unilaterally. The European and Asiatic blocks have doubtless for a long time endeavoured to reach the equator, and thus are thrust southwards relative to the sima. Moreover, they probably take part in the general westerly drift of the continents. ”

“ The conception of Haug, who wishes to consider the whole of the Atlantic as an enormous geosynclinal and the mid-Atlantic bank as the beginning of its crumpling, is nowadays regarded by most people as insufficient. The reader need only be referred to Andreé’s criticism. [18] According to the displacement theory, it is the former floor of the rift-valley which was in existence during the period when the Atlantic Ocean was composed of a relatively narrow fracture, which was subsequently filled with sunken margins, shore deposits, and also partly with molten sial. ”