Abstract
LONDON. Geological Society, June 7.—Dr. J. E. Marr, F.R.S., president, in the chair.—The microscopic structure of minerals forming serpentine, and their relation to its history: Prof. T. G. Bonney and Miss C. A. Raisin. The authors embody their investigations in the following conclusions:—(1) That both a tint and pleochroism are accidental rather than essential characteristics of antigorite. (2) Neither are low polarisation-tints characteristic, unless two mica-like minerals exist, otherwise indistinguishable. (3) That it is doubtful whether any hard and fast line can be drawn between antigorite and the more fibrous forms in ordinary serpentine rocks. (4) That the most typical antigorite appears when the rock has been considerably affected by pressure, but it becomes less so when the latter has been very great. (5) That so far from the nearly rectangular cleavage of augite originating the “gestrickte struktur,” it is worse preserved than any other original Qne in the process of serpentinisation. Typical antigorite, how ever, apparently is rather more readily produced from augite than from the other ferromagnesian silicates, but is more directly a consequence of pressure than of chemical composition.—The tarns of the Canton Ticino: Prof. E. J. Garwood. The lakes dealt with comprise the larger Alpine tarns which occur in the Canton Ticino. Most of these drain into the Ticino basin; one or two, however, flow into the Reuss or the Rhine. These lakes owe their origin, when they are rock-basins, to the presence of lines of weakness, along which in many cases solution has taken place, while in some shallow tarns ice may have removed detached fragments; but in no case has a lake been found which can reasonably be assigned to ice-excavation inde pendent of rock-structure.
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Societies and Academies . Nature 72, 215–216 (1905). https://doi.org/10.1038/072215a0
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DOI: https://doi.org/10.1038/072215a0