Petrography and Geology of the Igneous Rocks of the Highwood Mountains, MontanaU.S. Government Printing Office, 1905 - 208 Seiten |
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Häufige Begriffe und Wortgruppen
ægirite albite alkali feldspars amount analcite analcite-basalt analysis anorthite apatite appears augite basaltic biotite borolanose breccias calculation cent character chemical composition Classification in prevailing color composed crystals dark described dikes diopside E. B. Hurlburt feldspathic feldspathoid femic ferromagnesian geologic grains granular groundmass H₂O Highwood Gap Highwood Mountains Highwood Peak Highwood rocks highwoodose hornblende igneous rocks intrusive iron isotropic Jour K₂O lavas leucite lime Little Belt Mountains magma mass material Megascopic microscope Mineral composition missourite mode Molecular molecules Montana montanose monzonite Na₂O nephelite norm nosean occur olivine orthoclase P₂O Palisade Butte petrographic phenocrysts Pirsson porphyritic potash present prevailing systems prisms pulaskose pyroxene salfemane salic sandstones seen Shonkin Creek Shonkin Sag laccolith Shonkin stock shonkinite shonkinose shoshonose shown silica SiO2 soda sodalite specimens Square Butte Subrang syenite system of classification texture TiO2 Total Trace U. S. Geol Weed zeolites
Beliebte Passagen
Seite 55 - Cascade formation the red shales contain bowlders and lenses of limestone varying from a few inches to a foot or more in thickness. The rock is dense, blue gray in color, weathering light buff, and contains numerous fresh-water fossils.
Seite 35 - DIKES. For field purposes the dark basaltic dikes may be divided into three classes according to the character of the prominent phenocrysts. In each case the base or groundmass is more or less dense and ranges in color from dark stone gray to black. The first class contains prominent phenocrysts of biotite up to half an inch in diameter and is composed of mica traps or minettes of Highwood type (phyro biotitic shonkinose). The second class has prominent phenocrysts of rather large, well-formed black...
Seite 50 - Square Butte is composed entirely of igneous rock. Above the sandstones of the table-land no sedimentary rock whatever is seen. Near the immediate contact of the igneous rock with the sedimentary strata the sandstone beds curve up sharply on all sides. Below this, where the trenching by the streams has gone on, the sandstones have been cut into and the intrusive sheets which form a peripheral fringe around the mountain are brought to light. These relations are shown on the map, PI.
Seite 116 - The augite is of a pale-green color with a tone of brown ; it is very fresh and clear, contains inclusions of ore and specks of biotite, and is entirely xenomorphic, though the orientation of the ore grains is at times zonal, thus indicating crystal planes. It has an excellent cleavage, and twinning bands pass through it in places; it does not show any pleochroism. The biotite is strongly pleochroic between a deep umber-brown and a pale yellow-brown; it is also entirely xenomorphic, though apt to...
Seite 52 - From what has already been said in regard to the platy parting which forms so marked a feature of Square Butte, it will be seen that it bears the same relation to the mass as a whole as do the enfolding leaves of an onion to the bulb cut in half by a horizontal plane. The parting planes are thought to represent parting surfaces parallel to the former covering of the laccoliths, from which the isothermal planes of cooling descended into the mass. The writer can conceive of no other hypothesis which...