The Origin of Continents and Oceans
THE ORIGIN OF
CONTINENTS AND OCEANS
THE ORIGIN OF
CONTINENTS AND
OCEANS
BY
ALFRED WEGENER
PROFESSOR OF GEOPHYSICS AND METEOROLOGY AT THE UNIVERSITY OF GRAZ, AUSTRIA
TRANSLATED FROM THE THIRD GERMAN EDITION
BY
J. G. A. SKERL, M.Sc.
WITH AN INTRODUCTION BY
JOHN W. EVANS, C.B.E., F.R.S.
PRESIDENT OF THE GEOLOGICAL SOCIETY
WITH 44 ILLUSTRATIONS
NEW YORK
E. P. DUTTON AND COMPANY
PUBLISHERS
PRINTED IN GREAT BRITAIN
PREFACE TO THE THIRD EDITION
The third edition is again completely revised and certainly differs nearly as much from the second as that did from the first.
The reason for this does not merely lie in that during the intervening two years an extensive literature has appeared which directly or indirectly concerns the displacement theory, but also particularly in that the entire substance of the book has been cast into a new and, as I hope, more convincing form, so that the essential may appear better separated from the non-essential portion of the work.
That the new edition has only the same size as the previous one has been mainly produced by a shortened treatment of palæoclimatology, which has now only been drawn upon in so far as it serves for the establishment of the displacement theory. My further studies on this subject I hope to deal with in collaboration with Professor Köppen in a special publication.[1]
In other respects also the present edition, like the preceding ones, bears traces of this joint work.
ALFRED WEGENER
Hamburg-Grossborstel
June, 1922
- ↑ J. W. Köppen and A. Wegener, "Die Klimate der geologischen Vorzeit." Berlin (Bornträger). In the press.
INTRODUCTION
There are few more fascinating problems awaiting solution than that of the extent and relations of land and sea in the past history of the earth. Innumerable maps have been published, constructed on the evidence afforded by the occurrence and distribution of marine and continental deposits of which the age has been determined, as well as on less substantial grounds, such as the supposed existence of an ancient land barrier between sediments containing marine faunas believed to be contemporaneous, but differing strikingly in their character. On the other hand, a close similarity between terrestrial faunas and floras in areas now separated by the sea has been usually considered as sufficient evidence of a former land connection since submerged beneath the waves.
In none, however, of these attempted reconstructions of the geography of the past has it been assumed that the positions of the continents relatively to one another has been substantially changed, though such a possibility has been suggested by more than one student of cosmogony.
It has been reserved for Professor Wegener to collect a body of geological data that go far to demonstrate that such a relative movement has actually occurred.
Not only does the present and past distribution of life on the land furnish powerful arguments in support of his contentions, but the succession of the sedimentary rocks in areas now separated by thousands of miles of sea show remarkable resemblances that can only be reasonably explained if these sediments were laid down in close proximity to one another and under practically identical conditions.
The evidence afforded by the variation from point to point of the gravitational and magnetic forces leads us to the conclusion that the oceans and continents do not simply represent, as was formerly supposed, local and temporary depressions and elevations of the surface, but correspond to essential differences in the composition of the earth’s crust.
The rocks of the continental masses consist for the most part of the acid plutonic rocks, granite and its foliated form gneiss. The sedimentary, metamorphic, and basic igneous rocks, though they often play a conspicuous rôle at the surface are essentially subordinate in amount. The continental rocks as a whole are comparatively low in density and are composed predominantly of silica, alumina, and the alkalis, and are sometimes referred to collectively as sial (that is to say, silica plus alumina). [Note.—Suess employed the term “sal,” but most people will agree with Professor Wegener in adopting a suggestion of Professor Pfeffer that the form “sial,” which has not, like “sal,” an irritating resemblance to the latin for salt, should be substituted.]
There is good reason for believing that the rocks forming the substratum of the ocean bed are more basic in composition and contain a large proportion of magnesia, iron oxide, and lime, and that similar rocks or magmas of the same composition underlie the sial of the continents and probably form a zone of the earth’s substance some fifteen hundred kilometres in depth. They constitute the sima (silica plus magnesia), in contradistinction to the sial.
The thickness of the continental sial is estimated by Wegener and others at a hundred kilometres, a figure which I am inclined to think is excessive. However this may be, it is Professor Wegener’s belief that the drifting of the continents is in effect a movement of masses of sial through the sima which slowly yields to their passage. He compares the physical character of the sima to sealing wax which may be regarded as an extremely viscous fluid. The viscosity (that is to say, the resistance to change of form) would, of course, be very much greater in sima, but in the course of the vast periods of the earth’s history it would yield in the same manner to continuously acting forces.
I am inclined to think that the most important distinction between the sial and sima lies in the fact that the magma from which the sial originally crystallised out owed its fluidity to the very large amount of magmatic water and other volatile constituents that it contained and when these have once been lost in the course of crystallisation, a far higher temperature than that of the original magma will be required to bring it once more into a fluid state. The sedimentary and metamorphic rocks are also as a whole difficult to fuse.
These considerations do not apply to the same extent to the sima. Basic magmas contain less water and there is not so much difference between the temperature of the original crystallisation of the rock and that required for remelting.
The sima could therefore be more easily brought into a molten or semi-molten state by a rise in temperature which might be brought about through the blanketing of the rocks by the deposition of sediments above them and by the depression that follows such accumulations, or simply, as suggested by Professor Joly, as the result of radioactivity.
Professor Wegener supposes that the sial originally covered the whole surface of the globe, but in the course of ages, as the result of folding, it diminished in area and increased in thickness, until in late Palæozoic and early Mesozoic times it formed a vast land area which he terms Pangæa. It included practically all the present continents, which subsequently separated and moved away from one another.
Professor Wegener also adopts the view, which has been advocated in various quarters, that the position of the poles on the earth’s surface has varied from time to time so that the same land area may at different times have experienced both polar and equatorial climatic conditions. On the evidence afforded by fossils and the lithological character of the rocks as to past climates, he has endeavoured to trace the movements of the poles from Devonian times to the present day. Previous authors had suggested that the glaciation in South America, India, and Australia at the end of the Carboniferous or beginning of the Permian was due to the neighbourhood of the antarctic pole, but the difficulty had to be faced that there was no possible position of the pole that was not distant at least 70° from one of the glaciated areas. This difficulty ceases to exist if Professor Wegener is right in supposing that all of them were at that time in close proximity to one another, instead of being separated by thousands of miles of sea as at present.
One of the most interesting questions raised by Professor Wegener is the possibility of actually detecting the relative movements of land masses at the present time by instrumental means. It has been contended that a series of determinations of longitude by lunars (observations of the moon’s apparent position relatively to the stars) show a gradual increase of the west longitude of north-east Greenland relatively to Greenwich. Everything depends on the accuracy of these observations and at present the general verdict appears to be one of non-proven. Observations by lunars at Godthaab (in west Greenland), in 1863 and 1882–3 appeared to show on the contrary a decrease of longitude of 2.6 seconds of time. In 1922, however, Lt.-Col. Jensen made a careful determination of the longitude by means of wireless signals from Nauen and observations of star transits with a 13.5 cm. theodolite and obtained a value nearly five seconds more than the mean of the previous determinations. He considered that this was a confirmation of the westward movement of Greenland. Colonel Sir Charles Close (“Geogr. Journal,” Vol. 63, p. 147, 1924), will not accept this on account of the unreliability of lunars. The observations by means of wireless are, of course, far more accurate, and another observation similar to that of Jensen, carried out say ten years hence, should enable a definite verdict to be obtained.
Professor Wegener also refers to the determinations of the difference of longitude between Greenwich and Cambridge, Massachusetts, by means of cable signals in 1872, 1892, and 1914. These show a minute apparent increase of .023 seconds. Such determinations, however, are subject from time to time to disturbing influences the true nature of which is uncertain and the effects of these are larger than the small variation in question. We shall, however, henceforth be in a far better position to determine whether any real changes occur. Every day the same wireless signals are received and recorded by both observatories (as well as by others on the two continents), and every clear night all the year round the time of transit of star after star is also observed. Observations for longitude are therefore now being carried out almost continuously and the effects of temporary abnormal conditions can therefore be eliminated, so that most authoritative and accurate results will in a few years be available.
Whatever may be the outcome of these observations and whatever modifications may prove to be required in the author’s views on the evolution of the present configuration of land and sea, he has done most valuable service in directing attention to a new and important element in the transformations that the world has suffered, an element which no one will henceforth be able safely to ignore.
I have elsewhere criticised some of the details of the author’s conclusions. It would be out of place to repeat these criticisms here. My only care has been to ensure that in this translation he should be allowed to state his own case in his own way. With this object the translation has been submitted to Professor Wegener and has been carefully revised by myself[1] and it may be regarded as an accurate and authoritative exposition of his views.
JOHN W. EVANS
- ↑ Perhaps I may be allowed to mention that the northern half of the map of South America (p. 50) reproduced from Keidel is itself an exact reproduction of that illustrating my paper on the rocks of the Rio Madeira, “Q.J.G.S.” vol. 62, p. 90, 1906, as Dr. Keidel himself has freely acknowledged.
NOTE BY THE TRANSLATOR
I desire to acknowledge the assistance kindly and freely given by Professor P. G. H. Boswell, his colleagues in the University of Liverpool, and Mr. C. P. Chatwin, F.G.S., in the progress of the work. The revision of the translation by the Author and Dr. J. W. Evans, F.R.S., has smoothed away many difficulties and considerably enhanced its value.
J. G. A. SKERL
University of Liverpool
June, 1924
CONTENTS
I. THE ESSENTIALS OF THE DISPLACEMENT THEORY
CHAPTER I
| 1 |
The congruency of the South Atlantic coasts as the starting-point of the Displacement Theory. The drifting movement of the individual continents. Reconstructed maps of the earth (Figs. 1 and 2 on pp. 6 and 7). Special kind of movement of India. Folding on the anterior margin of the drifting blocks. Westward drift of the continents. The drift from the poles. The lag of the island festoons. Continental blocks and the floors of the oceans. Historical notes. Approximations to the Displacement Theory by previous writers.
CHAPTER II
| 11 |
The contraction theory. Sheet-folding (over-folding) in the Alps. The compression cannot be explained by cooling. The shrinkage of a great circle cannot take place at a single place. The continental blocks cannot be explained by the contraction theory. The necessity of replacing the contraction theory by that of displacement. The doctrine of land-bridges. The doctrine of the permanence of oceans. The shallow water origin of the marine sediments on the continental blocks. The disposal of the mass of oceanic water in the reconstruction of the submerged bridging-continents. Isostasy. Its demonstration by gravity measurements. Summary.
II. DEMONSTRATION
CHAPTER III
| 28 |
The two frequency maxima of the altitudes of the earth’s crust. Continental blocks and floors of the oceans as two different layers of the body of the earth. Principles of earth magnetism. Velocity of earthquake waves. Dredged samples. Sima and sial. Thickness of the continental blocks according to Hayford and Helmert. Specific gravity of sial and sima. Smoothness of the ocean floors. Absence of folded mountains on the floors of the oceans.
CHAPTER IV
| 42 |
Width of the Atlantic Rift. The Zwarte Berge in Cape Colony and the Sierras of Buenos Aires. The eruptive rocks of Brazil and South Africa. Sediments of Brazil and South Africa. African origin of the Permo-Carboniferous erratics of South Brazil. The direction of folding of the gneiss massifs of South America and Africa. Regional movements of South America after the break. The Atlas Mountains without an American continuation. Character of the Atlantic Islands. The Carboniferous (Armorican) foldings in Europe and North America. Silurian-Devonian (Caledonian) folding. Algonkian foldings. Terminal moraines of the Pleistocene ice-caps. The convincing character of the independent controls. Basaltic zones of Greenland and Northern Europe. The Old Red in North America, Northern Europe, Greenland. Intrusive rocks in Greenland and North America. Lateral displacement of the masses of Grinnell Land and Greenland. Explanations with regard to the reconstruction of the pre-Atlantic connections of the continents. Abrolhos Bank. The Niger delta. The Newfoundland block. Iceland. The submarine bank in mid-Atlantic. Madagascar. India. The compression of Lemuria into the Himalayas. Australia. New Zealand. The collision of the Australia-New Guinea block with the Sunda Archipelago. Tasmania and East Antarctica. West Antarctica and the Drake Straits.
CHAPTER V
| 73 |
The views of twenty specialists on the land-bridges. Late age of the Atlantic. Evidence of earthworms. Reptiles and mammals of both sides of the North Atlantic. Carboniferous fauna. Examples of other affinities. Faunal and floral affinities of both sides of the South Atlantic. Juan Fernandez. Hawaian Islands. Lemuria. The three components of the Australian fauna.
CHAPTER VI
| 90 |
Organic evidences of climate. Inorganic evidences of climate. Spitsbergen as an example of an alteration from a tropical to a polar climate. Alteration of the climate of Central Africa from polar to tropical. The hypothesis of the wandering of the poles. Former attempts to verify the hypothesis of the wandering of the poles. Inexplicability of the Permo-Carboniferous glacial phenomena. Solved by the displacement theory. Ice, Glossopteris flora, coals, rock-salt as evidence of climate in the Permo-Carboniferous. Provisional position of the poles for the periods after the Carboniferous and up to the present day. The Quaternary glaciation of North America and Northern Europe.
CHAPTER VII
| 112 |
The absolute duration of the geological periods. The amounts of the annual displacements to be expected. The increase of the distance between Greenland and Europe. The question of the variation of the difference of longitude between Europe and North America. The secular alteration of latitude of the European and North American observatories.
III. ELUCIDATION AND CONCLUSIONS
CHAPTER VIII
| 120 |
Immersion equilibrium (Isostasy) of the earth’s crust. Shifting of the poles of rotation. Transgressions and Regressions (of the sea) caused by wandering of the poles. The coefficient of viscosity of the earth according to earthquake observations, the tides of the solid earth, and the oscillations of the poles. Possibility of a magmatic layer (asthenosphere). Influence of the great size of the earth. Paradoxical properties of viscous bodies. Soft solid, and hard fluid bodies. Temperature distribution in the earth’s interior.
CHAPTER IX
| 138 |
Extension of the floor of the sea by the drifting apart of the continental blocks. Depths and covering of the floor of the oceans. Possible explanation by the temperature relations. Currents in the sima. Deep-sea troughs.
CHAPTER X
| 146 |
Outlines of the continental blocks. Section through the layers of the earth. Insignificant importance of the sedimentary strata. The original complete covering of the earth with sial. Gradual decrease of folding in the earth’s history. The irreversible character of the evolutionary processes of the sial-layer. Inclusions of sima in the sial. The nature of vulcanicity.
CHAPTER XI
| 157 |
Development of the explanation of folded ranges by compression. Evidence of the gravity measurements. Folding and erosion, subject to the preservation of isostasy. Unsymmetrical character of the folding process. Greater thickness of the sediments in folded regions. Folding on the anterior margin of the drifting blocks, and equatorial folding. General conditions for normal folds, echeloned folds, lateral displacements, and rifts. The East African rift valley. Foundering of the Ægean Sea area. Predominant meridional rifts.
CHAPTER XII
| 173 |
The disturbance of gravity on the margin of continents. Pressure-relations. Formation of fiords. Submarine continuations of river-valleys on the Atlantic coasts. Festoons of islands. Echeloned festoons. Their geological structure. The bulging form of the coasts behind the East Asiatic festoons. Richthofen’s explanation of the festoons. Sliding coastal ranges. The Peninsula of California and the earthquake fault of San Francisco. The continental margin of Further India. Pacific and Atlantic types of coast.
CHAPTER XIII
| 190 |
The drift from the poles of the continental blocks. Their westward drift. Meridional rifts. Nature of the force causing the drift from the poles, and its mathematical expression. Westward directed forces. Forces derived from the deviation of the figure of the earth from the ellipsoid of rotation. Similar forces in the geological past. Cause and effect.
| 207 |
LIST OF ILLUSTRATIONS
Reconstructions of the Map of the World for Three Periods according to the Displacement Theory |
6 |
The same Reconstructions as in Fig. 1, but in another Projection |
7 |
Section through the Lithosphere according to the Doctrine of Isostasy |
25 |
Hypsometric Curve of the Earth’s Surface, after Krümmel |
29 |
The Two Frequency Maxima of Elevation |
30 |
Diagrammatic Section through the Margin of a Continent |
31 |
Diagrammatic Section through the Margin of a Continent |
37 |
Trend Lines in Africa, after Lemoine |
48 |
Diagrammatic Tectonic Map of South America, after J. W. Evans and Keidel |
50 |
Geological Map of North-west Greenland, after Lauge-Koch |
58 |
The Lemurian Compression |
64 |
The Scattering of the Chains of Islands by New Guinea, Diagrammatic |
67 |
Depth Chart of the Neighbourhood of New Guinea |
67 |
Depth Chart of the Drake Straits, after Groll |
71 |
Votes on the Question of the Four Post-Cambrian Land-Bridges |
75 |
Distribution of North Atlantic Organisms, after Arldt |
81 |
Evidences of Climate in the Permo-Carboniferous |
100 |
Carboniferous Folds and Position of the Equator, after Kreichgauer |
103 |
The Position (Latitude) of Central Europe in the Course of the Earth’s History |
110 |
Reconstruction of the Continental Blocks for the Great Ice Age |
111 |
Transgressions and Regressions caused by the Wandering of the Poles |
124 |
Transgression, Regression, and Wandering of the Poles between the Lower Devonian and Lower Carboniferous |
125 |
Transgression, Regression, and Wandering of the Poles between the Lower Carboniferous and Upper Permian |
126 |
Map of the Oceanic Sediments, after Krümmel |
139 |
Madagascar and the Seychelles Bank |
142 |
The Fiji Islands |
142 |
Section through the Yap Deep (after G. Schott and P. Perlewitz) |
144 |
Map of the Continental Blocks on Mercator’s Projection |
147 |
Section along the Circumference through South America and Africa |
148 |
Former and Future Hypsometric Curves of the Earth’s Surface |
153 |
Section through a Sial Block |
153 |
Gravity abnormality beneath Mountain Ranges, after Koszmat |
159 |
Compression without Disturbance of Isostasy |
161 |
Folding or Rifting as the Result of Differently Directed Movements of the Blocks |
166 |
The East African Rift-valleys, after Supan |
167 |
Rifting (Diagrammatic) |
170 |
Extensive Collapse due to the Stretching of the Lower Crust (Diagrammatic) |
172 |
Disturbance of Gravity on the Margin of a Continent, after Helmert |
174 |
Effect of the Pressures on the Margin of the Continent (Diagrammatic) |
176 |
Festoons of North-east Asia |
179 |
Manner of Origin of Island Festoons |
182 |
California and the Earthquake Fault of San Francisco |
185 |
Movement of One of the Surface Elements Intersecting the Fracture, after Lawson |
186 |
Depth Chart of Further India |
187 |
Level-Surfaces and Curved Plumb-line |
195 |
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This work is in the public domain in the United States because it was published before January 1, 1929. This work may be in the public domain in countries and areas with longer native copyright terms that apply the rule of the shorter term to foreign works.
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