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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eek, north-east of Pilot Peak, by the hydraulic method. The gold was mostlyangular, and came chiefly from a white dike of Tertiary quartz-porphyryor rhyolite. On the slope west of Mohawk Valley, two miles south of Wash post-office, is Bennetts hydraulic gold gravel mine. The bed rock is granite.On the north side of the ravine the material lying on the granite isseen to be made up of clay considerably compacted, with numerouspebbles and bowlders, w hich are generally well rounded. On some ofthem scratches were evident. The upper material was composed ofsand and gravel, with many fragments of granite, and of pre-Creta-ceous and Tertiary volcanic rocks. Traces of a rough stratificationwere noted. The material is supposed to be part of the higher terracesof the Pleistocene Mohawk Lake, and to have been furnished by theglaciers on the slope above, and therefore to be partly morainal. Four miles due west from the summit of Mount Ingalls, on the top of Am. Jour. S<i., Vol. XI.VII, p. 473.
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TURNER.) PLEISTOCENE DEPOSITS. 597 the ridge east of Little Grizzly Creek, is an area of andesitic breccia,at the south end of which is a small mass of the dense older basalt.Lying on the andesite and on the underlying Carboniferous rocks of theeast slope of tbe ridge is a moraine like mass of rubble, including manygranite bowlders, and some of the older basalt which may easily havecome from the small area on the ridge just south of the andesite. Thegranite bowlders are particularly abundant northeast of the north endof the andesite area They may have been formerly embedded in thefraginental andesite, although their distribution suggests strongly amorainal origin. A glance at tbe geologic map, however, will show thatthis origin is difficult to explain, unless the moraine (?) be supposedto exist before the eruptions of tbe basalt that forms the upper halfof the mountain. There is no granite exposed in the drainage basinon the flank of which the moraine-like mass is situated, but the gr

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