Abstract
LONDON. Geological Society, Oct. 23.—R. D. Oldham: Histone changes of level in the delta of the Rhone. (1) At the opening of the Pleistocene period the whole area was covered by a deposit of gravel and well- rounded boulders, over which the Rhone and its tributaries wandered, with no fixed bed and with a velocity of current that gave them a torrential character. (2) A period of subsidence followed, the gradient and the speed of current were diminished, and an alluvial delta built up, which was at least as extensive as that of the present day. Two stages can recognised in this deposit. (3) A period of uplift then set in, and the land rose, not less than 14 metres, above the level to which it had sunk, the deposits laid down were exposed to denudation, and an undulating surface of erosion was developed. On this weathered surface the settlements and structures of the Romans were erected. (4) Finally came another period of subsidence, which took place at intervals. One of these periods of subsidence probably took place between the years 1000 and 1500 B.C. The next change took place in the course of the eighth and ninth centuries; it amounted to about 5 metres vertical displacement. Finally, there was a fresh movement of subsidence, practically completed during the later half of the eighteenth century. The total amount of these movements of subsidence was about 10 metres, and at the end of them the land still stands about 4 metres, or more, above the lowest level reached before the period of uplift set in.—R. W. Pocock: The Petalocrinus Limestone horizon Woolhope (Herefordshire). The crinoid Petalocrinus has been recorded from Sweden and North America, but not hitherto from Britain. Its most striking peculiarity is the fusion of the arms into five solid arm-fans or petals, which radiate from the dorsal cup. The arm-fans are usually found detached the limestone, throughout which they are profusely scattered. A bed of large tabulate corals on which the Petalocrinus band rests is found in this association throughout the outcrop. The combined thickness of the crinoid and coral-beds varies between 3 in. and in. Liandovery rather than Wenlock affinities are indicated by the fauna of the transition-beds. The area appears to have been subjected to pressure, mainly along a north-west and south-east axis, developing thrust-faulting approximately at right angles to that axis; a late Coal Measure age is suggested for the principal movements. At May Hill and at Malvern the Petalocrinus Limestone with its associated coral-beds has been detected at the same horizon as at Woolhope.—P. K. Ghosh: The Carnmenellis granite: its petrology, metamorphism, and tectonics. This granite, which occupies an area of some 50 square miles between Falmouth and Camborne (Cornwall), was divided by the Geological Survey into (1) an earlier coarse variety and (2) a later fine variety. The coarse granite of the Survey has been subdivided into three types, which prove to be three distinct intrusions. The petrological characters of the granites and their differentiates are described. Analyses have also been made of the associated metamorphic rocks; these consist of ‘reen-stones’ slates, and schists of various types, as well as inclusions of country-rock within the granite.
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Societies and Academies. Nature 124, 744–746 (1929). https://doi.org/10.1038/124744b0
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DOI: https://doi.org/10.1038/124744b0