Laman utama Quarterly Journal of the Royal Meteorological Society Theory of Continental Drift : A symposium on the origin and movement of land masses both...
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REVIEWS 101 grefitest importance. Dr. Smith concludes his lecture with a brief description of the lines of investigation which have been pursued t o this end. The London Convention (1914) for the safety of life a t sea not only providcd for the inauguration of a n international derelictdebtruction, iceabservation and ice-patrol service, but also advised the application of scientific research to the ice problem. T h e various lines of research followed include the determination of the variation with place and time of the temperature and salinity of the sea water and the detection of icebergs by echoes from sound beams. T h e lecturer states, however, that attempts to overcome the problem of fog and ice cannot yet be regarded as very successful. From the point of view of meteorology there is little in either lecture to appeal to the reader who is not interested also in the general applications of physics to the problems of aeronautics and navigation. Either lecturer, however, with more time a t his disposal could have shown that meteorology plays a not unimportant part in the problems with which 17. E. he n-as denling. Theory of Continental Drift : A symposium on the origin and movement of land masses both iiiter-continental and intra-continental, as proposed by tlljred Wegcner. By W. ;\. 3. M. van WATERSCHOOT van der GRACIIT,BAILEYWILLIS, ROLLINT. CIIAMBERLIN, JOHN JOLY,G . .\. F. MOLENGRAAFF, J. \V. GREGORY, ALFRED WEGENER, CHARLESSCHUCIIERT, CHESTERR. LONGWILL, FRANKBURSLEY ‘rAYI.OR. WILLIAM B.O\VIE, DAVID WiIITE, JOSEPII T. SINGEWALD, Jr., W. DRRKY.Published by the American Association of and EDWARD Petroleum Geologists, Tulsa, Olclahonia, U.S.A. London (Thomas Murby and Co.), 19-18. go. Pp. S+240. T h e publication of the third edition of Wegener’s “ Origin of Continents and Oceans,” followed immediately by Kiippen and Wegener’s striking book Tlie Climates of the Geological Past, raised a greater volume of discussion than any other geographical work of the present century. This may have been due in par; t to the general revival of interest in the whole science of geophysics, but it must be attributed mainly to the startling nature of the theory itself, for continental drift o n the scale advocated by Wegener strikes a t the root of many oldestablished conceptions of geology. Hence the American Association of Petroleum Geologists is to be congratulated o n its enterprise in arranging this important symposium of international opinion on the subject. T h e fourteen contributions, some, including the long introductory exposition by Waterschoot van der Gracht, distinctly favourable, others as definitely antagonistic, a r e impossible of review in detail, but because of its importance for the science of past climates, the reviewer may be permitted to give his impressions of the position in which the symposium leaves the problem. I t is now well known that the earth’s crust is composed mainly of two dissimilar materials, known for convenience as sial and sima. Sial is the material of the great continental blocks; it is a little lighter than the sima, which underlies the continents and forms the floor of some a t least of the great oceans. Sial, typified by granite, is a true solid; sima, best known in the form of basalt, answers as a solid to any tests to which we can apply, but under enormous pressures it is believed that it can behave as a fluid-sometimes ; the significance of the qualification will appear later: At these times the continents may be regarded as plates of wax floating in a sea of treacle, a n d if the forces acting on them a r e sufficient, they can drift. There a r e several arguments in favour of ‘their having actually drifted. Mountain ranges like the Alps, the Andes and the Himalayas have resulted from the compression of great stretches of country, slabs REVIEWS 162 of continent having been piled one on another until the margins of the folded zone have approached several hundreds of miles ncarcr together. Similarly, the great African Kift V:iliey apparently represents the beginning of a split along the length of Africa. Another argument, which forms the starting point of, Wegener’s ‘ I Origin ” is the remarkable similarity of outline between the Americas on the one side and EuropeAfrica on the other. Arguments are many; the great g a p in Wegenw’s exposition is the lack of a force which is capable of moving mountains. Although theoretically, and under certain conditions, a fluid, the sima a t present offers a resistance on which the puny tidal and gravitational forces invoked could not make the slighzest impression; effectively it is a solid. Here comes in a theory elaborated by J. Joly, whose recent ‘ I Surface Origin ” as a History of the Earth ” surpasses even Wegener’s romance of science. The earth’s crust contains radio-active matter, and this generates heat. The heat generated in the continental blocks can escape through the surface, but if the calculations a r e correct, the heat generated in the great thickness of sima is more than the surface as now constituted can dispose of, even under the oceans. The sima must become continuously hotter, with the inevitable result that it must melt. Fusion begins at a great depth, and extends gradually upwards until it reaches nearly to the surface. Loss of heat can now proceed more rapidly, and the upper part of the ocean of sima begins to solidify. These cooled masses are heavier than the liquid sima, and sink to the bottom, the process continuing until the whole mass is again solid, when the heating up recommences. A complete cycle runs into many millions of years, commensurate with a geological period. Joly’s brilliant conception explains much. When the sima is liquid, it is light, and the continents sink down into it, causing periods of great marine transgression. As it solidifies and contracts, the continents rise high, and the stresses of contraction throw their margins into the great folds of mountain ranges. During the periods of fusion the sima offers a greatly decreased resistance to continental drift, while the tidal movements within it a r e exaggerated, and so provide the occasion as well as the opportunity for such drift. Moreover it appears that such drift is necessary to provide a n outlet for the heat generated in the sima below the continents, which would otherwise melt beneath our feet. None the less, the forces available apparently remain inadequate to their gigantic task. This applies especially to the gravitational forces acting towards the equator, on which Wegener relies for the breaking up of his great antarctic “ Pangaea ” over which developed the Permo-Carboniferous ice sheet of the southern hemisphere. Relative east-west movements of the continents have some, though speculative, geophysical basis ; north-south movements rest almost entirely on arguments as to past climates. Several contributors to the symposium consider that Wegener’s treatment of this aspect of the problem, though ingenious, is open to many grave objections. Moreover the mechanism described by Joly, which does so much to make the east-west movements more plausible, also necessitates great changes in the heights of the continents, and the proportions of land and sea, which would involve corresponding changes of climate, of which Wegener takes little account. The able geologist who opened the discussion sums up a t the end. Generally Speaking, he favours the theory, but he concludes : “ This entire symposium stands as a token of the insufficiency of what we have been teaching in the past to explain the facts, and also, of our inability to make our new attempts at an explanation fit in with everything which we now believe to be a fact either in geophysics, geology or biology. . . . T h e more deeply we think and search, the more the problems multiply. .” C. E. P. B, ..