United States or Cambodia ? Vote for the TOP Country of the Week !
GNEISS is the general name under which are comprised coarsely foliated rocks banded with irregular layers of feldspar and other minerals. The gneisses appear to be due in many cases to the crushing and shearing of deep-seated igneous rocks, such as granite and gabbro.
The rock has probably been derived by dynamic metamorphism, from a coarse igneous rock like a gabbro. 7 Epidotic Sericitic Schist. Washkagama Lake. A fine grained compact gray rock, of aggregate structure, consisting chiefly of quartz, plagioclase and biotite, and the alteration products epidote and sericite.
The one exception is on Caribou Ridge, which is capped by a much altered gabbro. The first noticeable change in the character of the country rock is a Washkagama Lake, where a fine grained epidotic schist was observed, having a dip 82 degrees W. and a strike S. 78 degrees E. At Otter Lake a much foliated and weathered phyllite was found. Strike N. 73 degrees E. and a dip of 16 degrees.
DIORITE, still less siliceous, is composed of hornblende and feldspar, the latter mineral being of different variety from the feldspar of granite and syenite. GABBRO, a typical basic rock, corresponds to basalt in chemical composition.
In the district of Glatz the fissures of the gabbro are filled with a steatite of a greenish white colour, and the rock which was long thought to belong to the grunsteins* is a close mixture of feldspar and diallage. Near Guanaxuato, in Mexico, I saw it alternating with syenite.
The higher hills west of Seal Lake are capped by a much altered gabbro that has undergone considerable weathering. Between the Nascaupee River and a few miles beyond Bibiquasin Lake the rock is quartzite, considerably weathered and covered by drift.
The quartz grains show secondary growth. 13 Altered Gabbro Thirty-two Miles Above Wuchusk Nipi on Nascaupee River. A coarse dark green rock whose principal constituents are pyroxene plagioclase and magnetite. There is a slightly developed diabasic structure and the rock is much altered by weathering; the resultant product being chlorite. 14 Quartizite Bibiquagin Lake.
This division corresponds with that proposed by Bunsen and Durocher for volcanic rocks, upon the results of analyses of a large number of specimens from various districts. Examples: Basalt, Dolerite, Hornblende rock, Diorite, Diabase, Gabbro, Melaphyre, and Leucite lava. Examples: Trachyte, Rhyolite, Obsidian, Domite, Felsite, Quartz-porphyry, Granite.
LABRADOR- ROCK is a term used for a compound of labradorite or labrador-feldspar and hypersthene; when the hypersthene predominates it is sometimes known under the name of HYPERSTHENE-ROCK. GABBRO and DIABASE are rocks mainly composed of triclinic feldspars and diallage.
Word Of The Day