Abstract
OF the forty-three papers presented to Section C this year, comparatively few are of lasting importance, geologists having apparently saved up their best work for presentation at Zurich, or else having exhausted themselves at the excellent and successful session of the previous year. The President's address, containing an excellent epitome of the recent progress of mineralogy, was rather fitted for quiet and thoughtful perusal than for reading to a mixed audience, but it will be looked back upon as one of the most valuable of the contributions to the forthcoming volume of Proceedings. It was followed up by only one paper dealing with pure mineralogy, that of Mr. H. A. Miers, on a new method of measuring crystals. The two fundamental laws of crystallography—namely, (1) the constancy of the angle in crystals of the same substance, and (2) the law of simple rational indices—seem to be violated by those crystals which are liable to irregular variations in their angles, or those which have the simple faces replaced by complicated “vicinal” planes. Both these anomalies are exhibited by potash- and ammoniaalum. Brilliant and apparently perfect octahedra of these salts show large variations in the octahedron angle; other crystals show low vicinal planes in place of the octahedron faces. If it be true, as is supposed, that the octahedron angle varies in different crystals, it would be interesting to ascertain whether progressive variations can be traced during the growth of a single crystal, and whether some or all of the octahedron faces change their direction in space if the crystal be held fixed during growth.
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Geology at the British Association. Nature 50, 411–413 (1894). https://doi.org/10.1038/050411a0
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DOI: https://doi.org/10.1038/050411a0