Abstract
IN the Mémoires de la Société de Physique et d'Histoire Naturelle de Genève (vol. xxxviii., pages 69-168) M. Louis Duparc and Mme. M. Tikanowitch continue their work on the Ural Chain by an account of its rocks to the east of the main watershed and in the upper basin of the rivers Kakwa and Wagran. This, the fourth of their contributions to the geology of that chain, is prefaced by a sketch of the physical features of the district, the illustrations to which show that it consists of huge hills rather than of rugged mountains. The rocks are partly sedimentary, arenaceous, or slaty argillaceous, with some quartzose crystalline schists; partly igneous. Of the latter a very complete petrographical study has been made, including chemical analyses of the principal types, several of which are very interesting. Among. those of deep-seated origin are the following: quartz-bearing micaceous diorites (evidently allied to tonalites) and gabbrodiorites (in which probably the hornblende is secondary), olivine-gabbros, and massive dunites. Besides these and serpentines, are tilaite (a variety of eucrite) and pyroxenites. This association is interesting, for it often exists, more or less completely, in other regions, and suggests certain modes of magmatic differentiation. The dyke-rocks include hornblendic berbachites and various dioritic porphyrites, besides amphibolites, in some at least of which the hornblende appears to be secondary. The article ends with a description of the crystalline schists which, however, do not appear to be of any unusual interest. The memoir, illustrated by twelve photographic figures of the microscopic structure of the more interesting rocks, forms a most welcome addition to petrology, the more remarkable when we learn the difficulties with which the authors had to contend in their three visits to this region, in consequence of the sparse population, the want of roads, and the absence of maps.
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Mountain Geology . Nature 95, 188–189 (1915). https://doi.org/10.1038/095188b0
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DOI: https://doi.org/10.1038/095188b0