Abstract
LONDON. Geological Society, June 27.—Sir Archibald Geikie, Sec.R.S., president, in the chair.—Interference-phenomena in the Alps: Dr. Maria M. Ogilvie Gordon. The present paper, so far as it deals with the general structure of the Alps, was completed in April, 1905, but the author has since endeavoured to strengthen her line of argument by taking as a type the series of structural changes undergone in the largely igneous mountain-massive of Bufaure in the dolomites. After describing in detail the geology of the Bufaure Massive, the structural relation of the Western Alps and the Engadine to one another and to the whole mountain-system are discussed. From the arrangement of overthrusts, as well as from the distribution of the igneous intrusions in the Western Alps and in the Engadine, it is concluded that these were areas where leading cross-faults intersected the east-and-west Central Alpine band, and shows how the coalescence of these cross- faults with E.N.E.—W.S.W. faults on the north side and W.N.W.—E.S.E. faults on the south side defined two leading fault-curves, the one passing through the Engadine, the other passing through the Western Alps. The cross-segment comprising the Rhine-Ticino district between the Western Alps and the Engadine is regarded as anticlinal in character, segments having been down-thrown from it both towards the west and east, and overthrust masses have crept E. and S.E. from the Western Alps and westward from the Engadine. The relation of the French Jura Mountains to the Alpine system is then discussed, and it is pointed out that the Swiss-French plain flanking the Western Alps presents the same essential features of structure in relation to the Western Alps on its east side and the French Jura Mountains on its west as those elucidated for the Rhine-Ticino cross-segment. The strike-curve round the west formed by the Jura Mountains and the ranges of Dauphin is interpreted as the peripheral plicational system in the Alps, showing that the region between the Hungarian basin and the mountain- groups of Central France has been under the influence of the westward thrust. The general principle of structure is the sagging of crust-blocks by means of normal faults towards bands or localities of crust-weakness or subsidence, and the reverse or overthrust-movements which may take place from within these bands or localities. The paper affords evidence of differential rates of move- ment in different parts of a thrust-mass or fault-block undergoing horizontal displacement, both in respect of the laterally-adjacent parts of a thrust-mass and also of the subjacent layers. The maps and sections show that the actual deformations which characterise a thrust-mass have a diffeient direction of strike on either side of an axial band of maximum horizontal displacement. Several examples in the dolomites are described where there has apparently been a local reversal of the regional westward movement. While each individual case demands special examination, an explanation that satisfies certain cases is provided. At localities where the base of the thrust-mass is open to inflows of igneous rock, the igneous material may ascend and be carried onward with the gliding mass. After consolidation of such igneous inflows, they present resisting bodies within the thrust-mass, which, in the same way as any massive developments of sedimentary material, impede the advance of rock-material in the same direction as before. The tendency is for the material of the thrust-mass to be plicated and faulted as it is driven against a resisting body, widening out in a direction parallel with the resisting mass, and piling up the material to such an extent that local reversal of the direction of overlapping is produced.—The influence of pressure and porosity on the motion of subsurface water: W. R. Baidwin-Wiseman. The author commences the paper with a brief historical summary of the researches which have been conducted since 1830 on the motion and behaviour of underground water. In discussing the influence of the porosity of a rock on the rate of flow of water through it, he describes the variations in porosity which may occur in restricted areas of the same rock, due to superincumbent pressure, faulting, and the intrusion of dykes. He describes experiments on the rate of desiccation and soakage of rocks. A lengthy series of laboratory experiments, conducted with specially devised apparatus to afford a constant pressure and to eliminate all errors due to lateral flow, are explained, and it is demonstrated that there is not a uniform relation between flow and pressure in rocks over considerable range of pressure. Various attempts at determining the range of the cone of depletion in strata are passed in review, and a method based upon an experimental determination of the variation of internal pressure in a rock-mass when charged with water and subjected to a considerable difference of pressure on the two faces is outlined. In the concluding portion of the paper data collected during various hydrological surveys are discussed, and the influence of surface-configuration and strati- graphical sequence on the subsurface water-contours are pointed out.
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Societies and Academies . Nature 74, 374–376 (1906). https://doi.org/10.1038/074374a0
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DOI: https://doi.org/10.1038/074374a0