File:Report of the geological exploration of the fortieth parallel (1870) (14565866817).jpg

Identifier: reportofgeologic01unit (find matches)
Title: Report of the geological exploration of the fortieth parallel
Year: 1870 (1870s)
Authors: United States Geological Exploration of the Fortieth Parallel (1867-1881) King, Clarence, 1842-1901 Hague, A. (Arnold), 1840-1917 Emmons, Samuel Franklin, 1841-1911 Hague, James D. (James Duncan), 1836-1908 Meek, F. B. (Fielding Bradford), 1817-1876 Hall, James, 1811-1898 Whitfield, R. P. (Robert Parr), 1828-1910 Ridgway, Robert, 1850-1929 Watson, Sereno, 1826-1892 Eaton, Daniel Cady, 1834-1895 Bien, Julius, 1826-1909, engraver
Subjects: Discoveries in geography Geology Mines and mineral resources Paleontology Botany Birds
Publisher: (Washington, D.C. : G.P.O.)
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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specimens have a granitoid look, suggesting some of the nevadites.While sanidin and biotite are the jji-ominent constituents, there appearsmall plagioclases, unaltered hornblendes, and considerable olive-coloredaugite, and the microscope reveals apatite and magnetite. In immediatecontact with the Lone Peak granite, the rock is an earthy, greenish-whitemass, with the feldspars kaolinized and the groundmass decomposed beyondrecognition. The western body of mountains beyond the Jordan consists also ofsanidin-trachytes, rich in glassy feldspar and bronze mica, and possessinga very little hornblende. Here at the northern limit of the main body, atRose Canon, hornblende and mica are more abundant and sanidin less.Throughout the middle of the group are dark, heavy, hornblendic tra-chytes, in which the proportion of plagioclase rises very nearly to equalitywith the sanidin, and the rocks approach the andesitic habit. Near Salt Lake City, about two miles up the canon of City Creek, Jiel i-M A
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2C o TRACHYTES. 591 the hills on either side of the stream are for a short distance (not overa mile and a half) formed of dark, reddisli-brovvn trachyte. All aroundthe sides of the body the Eocene Tertiaries are extremely soft, andthe earthy accumulations effectually hide the relative ages of the two.There is little doubt, however, that the trachyte, like that east of the moun-tain, is more recent than the Eocene beds. This outburst is directly onthe line of the great fault, which to the south has cut off the ends of thePalajozoic and Mesozoic strata, and to the north has spHt down the bodyof Archsean rocks which forms the nucleus of the range. The rock shadesfrom reddish-gray into hght pinkish-gray, deepening in some cases into adark chocolate. It has a rough, coarsely crystalline groundmass of feld-spar, hornblende, and biotite. Among the macroscopical crystalline secre-tions are abundant sanidin and a high proportion of plagioclase, deep-brownhornblende with the characteristic blac

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