. Report of the geological exploration of the fortieth parallel . , which are of frequent occurrence along theFortieth Parallel; thatis, itis a compound of quartz, biotite, hornblende, ortho-clase and plagioclase feldspars, and titanite, with a relatively large proportionof plagioclase, liornblende, and titanite. The crystals of titanite can bereadily seen by the naked eye, and are frequently quite large and of veryperfect form. By the aid of the microscope, pale-green hornblende micro-lites are found Avithin all of these crystals; apatite is found to be abundantlydisseminated through the mass
. Report of the geological exploration of the fortieth parallel . , which are of frequent occurrence along theFortieth Parallel; thatis, itis a compound of quartz, biotite, hornblende, ortho-clase and plagioclase feldspars, and titanite, with a relatively large proportionof plagioclase, liornblende, and titanite. The crystals of titanite can bereadily seen by the naked eye, and are frequently quite large and of veryperfect form. By the aid of the microscope, pale-green hornblende micro-lites are found Avithin all of these crystals; apatite is found to be abundantlydisseminated through the mass, and, in some varieties, plates of red oxide ofiron; the larger hornblendes are also seen to be made up of accumulationsof single prisms, and the qmirtz to be comparatively poor in licpiid-inclu-sions. An analysis of this granite made by Prof Thomas M. Drown givesthe following constituents: Silica Alumina Ferrous oxide. Manganous oxide Lime Magnesia Soda Potassa . Ignition U S- Geol-Ezpl 40Parallel PLATE XV. ^ GRANITE AND ARCHiEAN ROCKS. 357 The granite of Lone Peak resembles this very closely, but shows alsoa porjjliyritical structure, carrying large crystals of dull white orthoclase iua crystalline matrix. In this, two principal sets of cleavage-planes, at rightangles to each other, are 2>iominentl} developed, giving the rock a tend-ency to separate into rectangular masses. Lone Peak itself is a narrowledge, rising about 1,500 feet above the general surface of the ridge, havingon its southern and western side a sheer perpendicular wall as straight as ifbuilt of masonry. This wall and the roche-moutonee basin which extends tothe southward from Lone Peak are seen in the colored view of Lone Peakin Volume I. La the narrow ravine at the mouth of Big Cottonwood Canon,where the granite spur of Twin Peak is denuded, a similar porphyriticalgranite is observed. It is rich in hornblende, biotite, and titanite, and underthe miscr
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