Bulletin of the Geological Society of America, Band 6The Society, 1895 Vols. for 1938-61 include as pt. 2 of the December issue the Society's Abstracts, later published separately. |
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Andere Ausgaben - Alle anzeigen
Häufige Begriffe und Wortgruppen
altitude anorthosites Antillean appears augite basin beds calcite Caprina carbonate channel character coal Coast ranges conglomerate containing creek Cretaceous crystalline delta deposits depth dikes dolomite drift east eastern elevation erosion evidence extended fault fauna feet feldspar figure fjords formation Fort Riley fossils Fusulina gabbro Geol geologic geologist glacial glaciers gneiss grains granite Highwood hills horizon hornblende ice-sheet igneous indicate intrusion islands Klamath mountains lake land layers limestone lithologic locality lower Magnesian Manhattan mass Meek metamorphism miles minerals Minnesota Miocene moraine mountains movement northern observed occur orthoclase paper plain plateau Pleistocene Pliocene portion pre-Cretaceous present probably Professor pyroxene quartz region river rocks Saint Lawrence sand sandstone schists serpentine Shakopee shales shonkinite shore side silica slope species Square butte strata streams submerged surface terraces thickness tion upper valley veins vertical writer
Beliebte Passagen
Seite 439 - The contact-metamorphism produced in the adjoining mica-schists and limestones by the massive rocks of the " Cortlandt series,
Seite 153 - I have of late years made while in charge of the Atlantic Coast Division of the United States Geological Survey, and...
Seite 19 - ... feet above the prairies at their base. Their structure has been thoroughly studied by Wolff, who finds that they consist of late Cretaceous strata, soft sandstones, nearly horizontal in stratification, intersected by a network of eruptive dikes. The more enduring igneous rocks have preserved this range, while an average denudation of not less than one mile in vertical amount reduced all the surrounding country to a baselevel of erosion.
Seite 19 - Glacial period there ntervened a second great epeirogenic uplift, as shown by a return of the conditions of vigorous stream erosion and a new cycle of partial baseleveling, by which wide flat valleys were cut in the eastern part of these Cretaceous plains.
Seite 19 - Tertiary era appears to have raised this portion of the plains to a height above the sea as great as the vertical extent of their Tertiary erosion — that is, to a height of at least 1,000 to 5,000 feet, increasing from east to west. Toward the end of this era the baseleveling had reduced the country mostly to a plain, which was probably only a few hundred feet above the sea, lying much below its present altitude. RENEWED ELEVATION AND PARTIAL BASELEVELING AT THE CLOSK OK THE TERTIARY AND DUUING...
Seite 74 - Ranges ; the State Geologist, considering all those chains or ridges of mountains as belonging to the Coast Ranges, which have been uplifted since the deposition of the cretaceous formation, while those, which were elevated before the epoch of the cretaceous, are reckoned as belonging to the Sierra Nevada.
Seite 19 - Arch can and Paleozoic rocks upon a large area bounded on the west by the escarpment before mentioned as forming the eastern limit of the plains. The duration of the earlier baseleveling apparently coincided as to both beginning and end with the Tertiary or Somerville cycle of partial baseleveling which Davis and Wood have studied in Pennsylvania and northern New Jersey and believe to have affected a large area of the other eastern states.
Seite 217 - The valleys in front of the glaciers are well floored with glacial wash, but even here the rock occasionally appears. Considerable delta-fans project into the gulf, but none of them exceed half a mile in depth. Consonant with this scantiness of drift, the topography of the borderland shows only moderate evidence of glacial subjugation. It is mildly rounded, but not greatly molded. ,ARE THE GLACIERS ADVANCING OR RETREATING? Several glaciers on Herbert and Northumberland islands showed evidences of...
Seite 18 - When its marine and lacustrine deposits were first raised to l>e dry land they had a monotonously flat surface. A very long cycle of baseleveling ensued, beginning as soon as this northern part of the plains was uplifted at the end of Cretaceous time and continuing nearly or quite to the end of the Tertiary era. During this time the surface was gradually lowered by the action of rains, rills, rivulets, creeks and rivers, until it was mostly reduced to a baselevel of subaerial erosion.
Seite 405 - We believe that they therefore represent parting surfaces parallel to the former covering of the laccolite from which the isothermal planes of cooling descended into the mass. We can conceive of no other hypothesis which would give a reasonable explanation of their arrangement and disposition, and since Square butte is unquestionably an intrusive mass we regard them as one of the strongest proofs of its laccolitic nature. Such an arrangement of the parting planes of a cooling igneous mass is by no...