IN CLOSING the meeting, I propose to make only a few brief observations. The discussions have confirmed the present paucity of quantitative data on displacements in continents, and most speakers have been at some pains to show how difficult it is to arrive at such data. Nevertheless, the attempt upon which the Geological Society is embarking is fully justified even if it only leads to a recognition of the orders of magnitude involved.
Professor Shackleton’s contention that the older orogenic belts differ in kind from the great circle of activity resulting from Wegenerian Drift had not been challenged as much as he had expected, perhaps because of our ignorance of what really happens in depth. Is it generally the case, for example, that the ancient orogenic belts no longer possess roots? If this is so, Professor Bott’s interesting study of the gravitational energy involved in dissipating a root becomes of much significance. It is far from being proved, however, that roots, even in the Tertiary-Recent orogenies, are universally present, and recent traverses of the western USA have yielded surprising results. The need for much more detailed surveying of the Mohorovi
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discontinuity is evident; the present stage is barely a first reconnaissance, but Dr Oxburgh’s contribution emphasized the possibility of valuable information from this source. Some time ago I asked whether the great ‘basin and range’ faults could be proved to displace the ‘Moho’, but the geophysicists of the U.S.G.S. were unable, from the available data, to answer this question.
Dr Phillips and Dr
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This 250-word extract was created in the absence of an abstract.
