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abundant acid alteration amount analysis angle appears arranged augite bands becomes beds biotite brown calcite called carbonate of lime cement cent character chemical chiefly clay cleavage coal color colorless common completely composed composition constituent contains County crossed crystalline crystals dark deposited Described developed evident extinction feldspar formation fragments frequently Geological glass grains granite green groundmass hornblende igneous illustrated inclusions indicate iron irregular larger layers less light limestone lines magnetite mass material matter mica microscope minerals minute nearly numerous occasionally occurs olivine optical organic origin oxide parallel particles pebbles phonolite places plagioclase plane portion present prisms probably produced pyroxene quartz refraction region represented result rock rounded sand sandstone seen separated shale shells shown siliceous solution sometimes Specific gravity specimen spherulites structure substance surface Survey thickness thin section tion trace twinning usually varies volcanic
Σελίδα 278 - The most striking feature in the texture of the unaltered gabbro is the repeated and abrupt change in the coarseness of the grain which is seen at some localities. It was undoubtedly caused by some irregularity in the cooling of the original magma from a molten state, for which it is now difficult to find a satisfactory explanation.
Σελίδα 128 - First, by diminution of the tension of the carbonic acid in the atmosphere ; second, by agitation of the solution." "Theoretically either one of three things may occur to the neutral carbonate of lime, if it be thrown out of solution by either one of these processes. The carbonate may be redissolved, deposited as a calcareous mud, or built into organic structures.
Σελίδα 375 - ... distributed the abundant folia of black mica. In the thin section the structure is cataclastic; that is to say, the various minerals of which it is composed have, since their formation, been more or less shattered and distorted through dynamic agencies acting upon the rock mass of which they form a part. Quartz and black mica are the most prominent constituents, though there are abundant feldspars of both potash and soda lime varieties. In addition to these are abundant accessory epidotes, a...
Σελίδα 376 - Boda solution (see p. 326). duced to yellowish brown shreds. The feldspars are in some cases opaque through kaolinization, but in others are still fresh and unchanged even in the smallest particles. The finest silt, when treated with a diluted acid to remove the iron stains, shows the remaining granules of quartz, feldspar and epidote beautifully fresh and with sharp, angular borders, the mica being, however, almost completely decolorized and resembling sericite more than biotite.
Σελίδα 117 - ... resembling the bastions of a fortress. The summit of the cliff is covered with gravel, but measuring from the top of the hill a short distance from the margin, the present thickness of this chalk is found to be about 135 feet from the summit to the bed underlying it. This chalk has a low southeastern dip. The regularity of this bed throughout its exposure — about one-fourth of a mile — and its reappearance a few miles to the east and across the Saline watershed, shows that it is not a local...
Σελίδα 77 - Its economic value above ground is great, but it is greater below. In its outcrops it is a source of the finest building stone and the best grindstone grit of the country; and when it dips beneath the surface it becomes the repository of invaluable supplies of petroleum, gas and salt water.
Σελίδα 118 - The fact that these are the only flint horizons, so far at least as is known to the writer, in the whole of the immense Cretaceous deposits of the United States, is very interesting, and especially since they occur about the middle of the Lower Cretaceous series instead of at the top of the Upper series, as in England.
Σελίδα 98 - this material is evidently now forming, and in places has been cemented into a compact oolite by the deposition of a paste of calcium carbonate between the grains, and forms irregular layers several inches in thickness that slope lakeward at a low angle.
Σελίδα 198 - No. 1. coarse theralite from Gordon's Butte, was made by WF Hillebrand in the laboratory of the United States Geological Survey, at Washington, and Nos. 2 and 3 by EA Schneider, in the same laboratory. Analysis No. 2 is of specimen No. 75, and No. 3 of specimen No.