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Theory of Continental Drift:

A Symposium on the Origin and Movement of Land Masses Both Inter-Continental and Intra-Continental, as Proposed by Alfred Wegener

By W. A. J. M. van Waterschoot van der Gracht, Bailey Willis, Rollin T. Chamberlin, John Joly, G. A. F. Molengraaff, J. W. Gregory, Alfred Wegener, Charles Schuchert, Chester R. Longwell, Frank Bursley Taylor, William Bowie, David White, Joseph T. Singewald Jr. and Edward W. Berry

Abstract

This publication was written in 1926 during an era of heated discussions on continental drift based on an AAPG Symposium of the same topic. The problem of continental drift raised considerable and spirited discussion in geological circles. Many authorities advocated it; others were undecided but favorably inclined; still others did not favor it, and some of those were violently opposed. The mere possibility of continental drift was firmly denied by some during this era. It was not possible to settle the problem, or even to discuss it thoroughly in a single publication, but the main principles of the theory of drift are covered as are the main theories of the time, offering an intriguing glimpse into the history of geologic approaches to continental drift.

  1. Page 1
    Abstract

    A brief outline is given of our present knowledge of the constitution of the interior of the earth and of the physical states of matter, which we have to consider. The insufficiency of the contraction theory to explain the surficial history of the earth, and particularly the problem of the major mountain chains, is exposed. The continental drift theories of F. B. Taylor, Alfred Wegener, and R. A. Daly are outlined in their latest aspect. Wegener’s views have been most widely published and worked out in the greatest detail. A discussion follows of the main arguments which have been proposed in support of the drift theories, as well as of some of the principal objections. The most serious of the latter is the lack of sufficient explanation for the mechanism of a drift of the magnitude of the acid continental crust (“sial”) over a solid, basic substratum (“sima”).

    A discussion of the theory presented by John Joly (1923-25), reaches the conclusion of a periodicity of fluidity and solidification of the basic (sima) substratum, caused by the generation of heat through radioactive changes in the atoms. This heat accumulates faster than it can dissipate into space, and through a period roughly estimated at 30 million years, will cause the sima sphere to become fluid under the outer sial crust. This should greatly increase the forces which tend to cause a locally differentiated westward drift of the outer crust and their effect, actual drift. In fact, if Joly’s thermal theory is right, such drift seems the only means by which accumulated heat can sufficiently be relieved and dissipated into space. It is calculated that, given sufficient drift, a period of 5 million years would suffice to re-solidify the basic substratum.

    These alternate periods of fusion and re-solidification are causally connected with the main world-wide diastrophisms, Joly’s “revolutions.”

    If Joly’s reasoning is correct, a general westward drift becomes a necessity, and a locally differentiated drift most probable. This would support the drift theories and eliminate the worst objection to them. There are, however, objections to some of Joly’s views.

    This is worked out and added to in greater detail; the author adds further conclusions of his own; the causes of relatively differentiated drift are discussed, not only as between the major continents, but also intra-continental, more local drift, its relations to isostasy, and the general continental deformation it must cause. Shifting of the earth’s poles need only be relative, and does not necessarily imply major changes in the location of the earth’s axis of rotation in space, thereby eliminating another objection against Köppen-Wegener’s plausible theory of geological climates. There is no necessity for dislocating the earth’s axis.

    The position of the author is as follows: he considers the theory of inter-continental drift worthy of very serious consideration and gradually has come to regard it ever more favorably. It offers a plausible explanation for several problems, never satisfactorily explained before. The results of further thought and geological research seem increasingly to support this theory, rather than to oppose it. Serious objections become ever more weakened by further research. In this spirit the theory is offered for serious discussion here in America, where, so far, it has found but scant support. The author realizes that no such theory is ever a finished product or perfect; he approaches it with an open mind and will welcome anyone’s argument in order to come nearer the truth. He offers his own thoughts and additions in the same spirit.

  2. Page 76
    Abstract

    After considering the theory of continental drift with avowed impartiality, the author concludes by means of geophysical, geological and paleontologic reasoning that it should be rejected, because the original suggestion of the idea sprang from a similarity of form (coast lines of Africa and South America) which in itself constitutes no demonstration, because such a drift would have destroyed the similarity by faulting, and because other contradictions destroy the necessary consequences of the hypothesis.

  3. Page 83
    Abstract

    A brief synopsis is given of the objections to the Wegener drift theory. It is not a general theory of earth behavior; it is a description of only one breaking up of a land mass, which does not satisfactorily fit the facts as now known and does not fit in the generally accepted record of geological time. The framework of the present continents was developed in pre-Cambrian time. Geological evidence does not show that a great continental mass split apart in comparatively late time. Geophysical evidence does not support the causes assigned to the drift displacement. The author indicates that the planetesimal hypothesis sufficiently explains the known crustal shortening of the earth. The planetesimal hypothesis is an integral part of comprehensive geological philosophy, but Wegener’s hypothesis is not.

  4. Page 88
    Abstract

    The thought is expressed that continental movement is not improbable during periods of fluid movement. A force sufficient to wrinkle the western side of North and South America would be competent to shift these continents as a whole.

  5. Page 90
    Abstract

    The author stresses the inadequacy of the hypothesis in that it postulates primarily a westward drift. He points to the mid-Atlantic ridge as the old line of separation from which America drifted west and Africa drifted east. A similar line of separation or great rift valley may now be forming in East Africa. The author is rather favorably inclined toward the drift theory, but he would not confine the movement to a westerly direction.

  6. Page 93
    Abstract

    The Wegener hypothesis would explain the distribution of land and water by lateral drift of the continents. The author believes the present distribution is more largely the result of vertical movements of the crust. He does not positively object to the hypothesis but points out that vertical movement or differential rising and subsiding of crustal blocks due to a shrinking earth would have the same effect as lateral drift.

  7. Page 97
    Abstract

    The author of the drift theory discusses geological climate in the United States and points out that one of the objections to his conception of land distribution, namely, the assertion of the presence of glacial deposits within his tropical belts, is not justifiable inasmuch as it is not positively known that so-called glacial deposits were really glacial. An advantage the drift theory has over all other geological theories is its susceptibility to verification by astronomical observations. Exact research is now being conducted that will throw more light on the theory.

  8. Page 104
    Abstract

    The following paper shows that Wegener’s attempt to fit the Americas against Euro-Africa leaves discrepancies of as much as 1,500 miles; that there is no fitting at all in the Central American region; that when Newfoundland is united with Ireland and the easternmost cape of Brazil fitted into the African Bight of Biafra, Central America is parted from South America by 1,200 miles, and Alaska from Siberia by 600 miles, leaving in the latter instance a deep ocean that is fatal to all inter-migration of marine and land life between these continents.

    It next explains that the tectonic structures and the faunal assemblages on either side of the Atlantic fit badly, that we have here only similarities and not identities, and that the faunas do not have more than 5 per cent of species in common instead of the 50-75 per cent called for on the basis of Pangaea. The detailed historical geology and stratigraphy of Newfoundland and Ireland, contrasted in adjacent columns, show that there are here no exact identities and few similarities.

    Finally, the writer discusses the small residuum of the Wegener hypothesis that has been becoming more and more apparent during the past fifteen years to all students of geosynclines and mountain structures, namely, that the continents appear to have moved horizontally and differently throughout geological time, but how much and in what directions are problems for the future. He also points out briefly how more harmony may be hoped for between geologists, paleontologists, and geophysicists working along these lines.

  9. Page 145
    Abstract

    Evidence so far advanced by advocates of the hypothesis is by no means convincing. Geophysicists recognize only tiny forces acting horizontally on the continents. The assumption that the sima is devoid of strength toward secular forces takes no account of mountain structure. Apparent coincidence of widely separated coast lines is probably accidental, as may be seen by comparison of Australia and the Arabian Sea. Petrographers, as well as stratigraphers and paleontologists, find that Wegener’s geological “controls” are not well established.

  10. Page 158
    Abstract

    In the first part of the paper, the author discusses the manner of formation of arcuate mountain ranges. Many leading geologists are advocating a wholly speculative hypothesis—the sinking of great sub-oceanic segments, with heavy landward underthrusts which cause folding and uplifting along the continental margin. With this mechanism they strive to account for the making of the circum-Pacific mountain ranges. They take no heed of Suess’ explanation, or of the facts which he advanced in support of his idea. The author presents his views with a careful discussion of the similitude of continental ice-sheets and continental crust-sheets. In the latter part of his paper, he discusses the interpretation of the principal features produced in Tertiary diastrophism and applies fundamental principles of earth sciences, and astronomy and cosmogony as well, to Asia and all the other continents as units of crustal movement.

  11. Page 178
    Abstract

    Wegener’s hypothesis is discussed by means of geophysical objections. Although it does not actually oppose the principle of isostasy, it does, nevertheless, possess features not in harmony with the idea that the earth’s crust in all parts is weak enough to be maintained in isostatic equilibrium by the constant action of gravity. The author raises questions about the hypothesis which suggest that it is not fully in accord with earth facts. If the earth material under the oceans is devoid of strength, why do such violent earthquakes occur in those regions, and why does the ocean floor maintain such pronounced relief? Why does Wegener collect so many of his floating sial masses in the northern hemisphere and why have some of the continents evidently moved away from the equator instead of toward it? Doubt is expressed about the shifting of the poles to the great extent postulated by Wegener.

  12. Page 187
    Abstract

    The Köppen-Wegener maps showing continental aggregates and climatic data throughout geological time, though clever, are open to serious criticism. If the continents could drift apart in geologically late time why did they not break up in earlier eras during greater diastrophic revolutions? Geologists should not forget the principle of isostasy.

  13. Page 189
    Abstract

    The two fundamental premises on which Wegener s displacement theory is based, namely, (1) the flotation of continents of sial on an underlying viscous layer of sima, and (2) the displacement of the continental sial by tangential forces, are both conceded by geologists. The disagreement is largely in the application of these premises to the solution of earth problems. Wegener makes a strong case on circumstantial evidence. But his reasoning is not wholly convincing. Despite objections raised to the theory, it possesses a great degree of probability and is supported by considerable evidence. The difficulties between Wegener and his opponents are largely because of disagreement as to the facts observed.

  14. Page 194
    Abstract

    The author objects to the Wegener hypothesis because (1) the method of presentation is not scientific, (2) the facts of geophysics do not support it, (3) it fails in explanation of geological climates, and (4) paleontologically it raises more distributional problems than it solves.

  15. Page 197
    Abstract

    The criticism which is voiced in this symposium is largely directed against Wegener’s conception of continental drift. The arguments can be divided principally into geophysical arguments about the possibilities and explanation of drift, and geological and paleontological arguments against the facts cited in support of Wegener’s drift and the consequences which a drift, such as the exponents of his theory sponsor, would be expected to have.

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