Annual report of the United States Geological Survey to the Secretary of the Interior . rhyolite-porphyries). No. 222S. ~ Plumas. B No. No. 384Plumas, d No. 153Plumas, d No. 288Plumas, d No. Silica Lime Potassa Soda 69 2,98 78 a Wedderburn, analyst. c Steiger, analyst. b Hillel>ran<l, analyst. d Hillebraud and Steiger, analysts. Jour, of Geology, Vol. Ill, p. 398. 648 GEOLOGY OF THE SIERRA NEVADA. Some brief descriptions of the microscopic features of these ro
Annual report of the United States Geological Survey to the Secretary of the Interior . rhyolite-porphyries). No. 222S. ~ Plumas. B No. No. 384Plumas, d No. 153Plumas, d No. 288Plumas, d No. Silica Lime Potassa Soda 69 2,98 78 a Wedderburn, analyst. c Steiger, analyst. b Hillel>ran<l, analyst. d Hillebraud and Steiger, analysts. Jour, of Geology, Vol. Ill, p. 398. 648 GEOLOGY OF THE SIERRA NEVADA. Some brief descriptions of the microscopic features of these rocks willbe fouiid in the authors paper in the Fourteenth Animal Eteporl Avery considerable portion of the quart z-porphyry series is much alteredand is quite schistose, the dip of the schistosity being often vertical. The relation of the quartz-porphyry breccia to the overlying greenstone tuffs on the east slope of the Sierra Buttes is described underthe heading Juratrias beds. A considerable portion of the quartz-porphyry of the Sierra Buttes and the ridge extending thence north to. FlG. 20.—Columnar Juratrins lava. Eureka Teak is regarded as a massive How, and as underlying the quartz-porphyry breccia beds. However, it can not be said that the field exami-nation was sufficiently thorough to determine whether this holds throughout the area. The breccia beds, moreover, contain some fragments andlayers of more basic lavas. One of these layers (No. 141 S. X.) exhibitsa columnar structure, thecolumns standing approximately vertical whilethe stratum as a whole dips at a considerable angle to the east. Thelocality is about one half mile southwest of I pper Salmon Lake. *0 is from a photograph of this columnar lava. Inderlying this stratum TURNER.] THE MAGNESIAN SERIES. 649 is a quartz vein dipping east at an angle of about 45°, along whichextends a dike or thin sheet from 8 to 10 inches in diameter. A tunnelhad been run in to exploit the quartz vein. Taken in connection with
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