The American Naturalist Volume 36, PT. 1

The American Naturalist Volume 36, PT. 1

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1902 edition. Excerpt: ...seems to have been norite and gabbro, diorite and granite. The last two rocks are connected by gradation phases, and this is thought to be evidence that their difference in age is not great. The peridotites and pyroxenites are mainly younger than the norites and gabbros, but some of the pyroxenites are apparently peripheral phases of the norite. The succession taken as a whole is supposed to "furnish an example of the occurrence of several rock types which represent the facies of a single magma and unite to form a geological unit." The serpentines were derived partly from the peridotites and partly from the pyroxenites. In the latter change the hypersthene and diallage first alter into fibrous hornblende, and this later passes into the serpentine. The area is very similar in its essential features to the Delaware area of gabbros described by Chester and the Baltimore area described by Williams.' The distinguishing features of the present area are (1) the abundance of diorite, (2) the comparative rarity of gabbro-diorite, and (3) the great abundance of pegmatite and granite dykes.1 Rock Structure.---The study of a series of andesitic and rhyolitic rocks that occur as extrusives in the Great Basin region suggests to Spurrs that the differences in structure of igneous masses may be brought about by slight changes in conditions under which crystallization took place. Among the differences which affect structure may be mentioned slight changes in the rate of cooling. Textural variations are less common in acid than in basic extrusives because in the latter the viscosity varies more rapidly with rapid cooling than in the former. The more important structures are not characteristic of particular rocks, but are the functions of the...
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Product details

  • Paperback | 162 pages
  • 189 x 246 x 9mm | 299g
  • United States
  • English
  • black & white illustrations
  • 1236985966
  • 9781236985965