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Societies and Academies

    Naturevolume 51pages406408 (1895) | Download Citation

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    LONDON

    Geological Society, January 23.—Dr. Henry Woodward, F.R.S., President, in the chair.—Carrock Fell: a study in the variation of igneous rock-masses. Part ii. The Carrock Fell Granophyre. Part iii. The Grainsgill Greisen, by Alfred Harker. The augite-granophyre of Carrock Fell was first described in its normal development, special attention being drawn to the various types of micrographic intergtowths which it exhibits. The variation of the rock was next examined, and, in particular, a curious basic modification which occurs near its junction with the gabbro described in a former paper. The granophyre here passes into a coarse type rich in augite, iron ores, and apatite, its silica-percentage falling to as low as 58. The author attributed this to the acid magma having incorporated in itself portions of the highly basic margin of the gabbro. The latter rock seems to have been fused or dissolved by the magma, with the exception of certain of its more refractory minerals which survive in the modified marginal part of the granophyre. The latter part of the paper dealt with a remarkable quartz-mica rock found on the north side of the Skiddaw granite. It differs in some respects from the Cornish greisens, and resembles in its mode of occurrence certain pegmatites in the Scottish Highlands. The author considered the rock to have been excluded from the granite in connection with the post-Silurian crust-movements of the district, while its competition has probably been further modified by subsequent chemical change.—The geology of the country around Fishguard (Pembrokeshire), by F. R. Cowper Reed.—The tract of country forming the subject of this communication occupies the northern part of Pembrokeshire, from Newport to Strumble Head.—On the mean radial variation of the globe, by J. Logan Lobley. The author submitted considerations (chiefly derived from the characters of the earlier sediments) which led him to suppose that crust-folds have not been produced by continuous contraction of the earth, and that the planetary heat and mean radius of the earth have been practically invariable during the period which has elapsed since Cambrian times.

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    https://doi.org/10.1038/051406c0

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