Identifier: annualreportofun1711geol (find matches)
Title: Annual report of the United States Geological Survey to the Secretary of the Interior
Year: 1880 (1880s)
Authors: Geological Survey (U.S.)
Subjects: Geological Survey (U.S.) Geology Water-supply Forest reserves Mines and mineral resources
Publisher: Washington : G.P.O.

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s Nose is a massive quartzite, and the relation of the gneisses andthe quartzite has been only superficially examined. No unconformityhas been proved to exist, but the writer expects during the field seasonof 189G to examine the contact more closely. The quartzite massreferred to is probably of the same horizon as that of Blue Mountain, tothe southeast. The age of the quartzite is uncertain, but there arenearly 10 milesof highly tilted sediments between the quartzite horizonand the pretty certainly Carboniferous limestone of Murphys. CaveCity, and Volcano, so that the quartzite may be much older than theCarboniferous. All of the rocks of the gneiss complex are thoroughly crystalline, andthere is thus far no positive proof that any portion of them represents 1 The Held inspection in 18DG brought out no evident proof of an unconformity, but bettor resultsare hoped for when the rocks collected are studied microscopically. U. S. GEOLOGICAL SURVEY SEVENTEENTH ANNUAL REPORT PART I PL. XXXIV
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((. SPECIMEN FROM GRANULITE DIKE, WITH QUARTZ BAND IN THE MIDDLE6. SPECIMEN FROM GRANULITE DIKE, WITH FELDSPAR BORDERS. TURNER.) GNEISSES. 701 original sediments. They are no more thoroughly gneissoid at thegranite contact than in the middle of the area, and the crystalline con-dition can not, therefore, be considered as a phenomenon of contactmetamorphism, unless it be supposed that this metamorphic action tookplace during an earlier period, perhaps when the rocks, now typicalgneisses, were deeply buried. In any case, the recrystallization musthave been brought about by more intense forces than those which havecaused the contact zones about the Juratrias granitic intrusions, ofwhich a good example is noted in the description of the Merced-Mariposa district. In a general way the strike of the gneisses is to the east of north,corresponding in this particular with the so-called Archean masses ofwestern Nevada. To the east is a large area of massive hornblendicgranite or quartz-mica dior

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