Page:The Journal of geology (IA journalofgeology11893univ).pdf/286
Below the magnetite-actinolite-schists and separated from the nearest exposure by a covered interval of 50 feet is the outcrop of quartzite discovered by Pumpelly and Credner. The outcrop runs about 175 feet along the strike and 30 feet across it. At the N. E. end the strike is about N. 55 °E, and at the S. W. end about N. 20° E., the dip in both cases being to the W. of N.,40°-45°. For the most part the rock is massive and heavily bedded, but the higher portion shows unmistakable sedimentary banding, and even false bedding.
In external appearance and in composition the rock is a very coarse-textured, light-colored quartzite, made up almost entirely of quartz, with some muscovite and chlorite as subordinate constituents. Under the microscope, probably because obliterated by shearing, no original rolled grains were seen, although several slides were examined. Red garnets are occasionally found in the quartzite.
A short distance south and west of the quartzite is a ridge running a little east of north, made up mainly of granite, which presents several bold faces to the west. Near the south end and on the west side, is found upon the granite a westerly dipping fringe of conglomerate, which extends some 50 feet along the strike, as a continuous rock mass. Farther north occasional small patches of conglomerate on the northwesterly sloping granite faces, indicate that the contact follows very closely the direction of the ridge, and lies near its western base.
III. Granite.
The granite exposed on this ridge occurs in both white and reddish weathering varieties, which appear to be, however, identical in composition and age. The rock is a coarse mixture of quartz and feldspar of which orthoclase is an important part, and which occurs in Carlsbad twins up to two inches in length. Light colored mica and biotite are largely developed in the planes of shearing. The granite contains much pegmatite, both in veins and in irregular masses. From the contact with the conglomerate back as far as exposures extend, the granite is