File:Annual report of the United States Geological Survey to the Secretary of the Interior (1895) (14801225153).jpg

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.
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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furnished the variegated pebbles referred to in the description ofthe Neocene river gravels of the Bidwell Bar and Dowuieville areas.Limestone, or more accurately marble, was seen at two points only, oneL.6 miles northeast, and the other 2.4 miles southeast of Milton, atboth places ( lose to the contact with the large granitic mass of thesoutheast corner of the Dowuieville area. The limestone contains yellow and reddish garnets and a wollastonite like mineral, presumably as a result of contact metamorpbism.There is, therefore, little doubt that the adjacent granitoid mass islater in age than the Milton formation. At the marble locality. -Amiles southeast of Milton, just at the contact, the granite rises a^ asteep wall above the level of the Milton sediments and the bedded rockappears to abut directly against the granite wall, the dip being easterly, that is. toward the granite. The hardened sandstone or qnart/iteof the series contains a good deal of an ant bigenio brownish-green mica
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TURNER.) MILTON FORMATION. 625 in minute foils, which may likewise be ascribed to metamorphisin.However, this body of sediments as a whole shows like evidence, bothmacroscopically and microscopically, of having been greatly com-pressed. Not only has very little secondary schistosity been devel-oped, but under the microscope the grains usually show little evidenceof crushing. The dip in the neighborhood of Milton is quite uniformto tbe east at 40° to 50°, with occasional dips as low as 25°. At thegranite contact it is in places much steeper. The Milton series seemsto rest unconforrnably on the presumably Paleozoic sediments that formthe mass of* tbe range in the Downieville area west of Milton. ThesePaleozoic (?) rocks consist of black slates, quartzite, and magnesiaulimestone. They stand approximately vertical and are much com-pressed. The difference in the lithologic character of the two sets ofrocks, the fact that one shows much evidence of dynamic metamor-pbism and the other com

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