Compte Rendu Volume 5

Compte Rendu Volume 5

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1893 edition. Excerpt: ...represented by a single color. Toward the east, notably along Sligo and Piney branches, these rocks are very massive, often quite devoid of any foliation, and are not infrequently filled with inclusion of other rocks in which characteristic granite contact minerals are largely developed. All this points to an eruptive origin, and these characters persist even where a secondary foliation has been developed in accord with the prevailing strike and dip. Farther westward the rocks appear more like typical gneisses, being banded, more micaceous, and more schistose. Apparent beds of conglomerate have also been noticed in them along the south bank of the Potomac river and near the Klingle Ford bridge over Rock creek. Diorite; massive, dark green amphibole-biotite-granite: These rocks present a marked contrast to the last type in their dark color. They always contain green hornblende, biotite, orthoclase, and plagioclase, sometimes one and sometimes tlie otber in excess. Quartz is also usually present and not infrequently rutile, sphene, and epidote as well. Under the microscope they generally show evidence of profound dynamic action. In all probability they represent ancient eruptive masses which have been subsequently greatly changed and recrystallized by earth movements. They are most extensively developed around Georgetown and near Cabin John. In quarries at the former place clearly defined inclusions of other rocks have been noticed, which substantiate the theory of their eruptive origin. Serpentine and steatite: A few small lenticular areas of serpentine and soapstone occur within the area under consideration. They are usually closely associated with the more basic hornblendic rocks, and are, probably, like these of eruptive origin, although this...show more

Product details

  • Paperback | 214 pages
  • 189 x 246 x 11mm | 390g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236510283
  • 9781236510280