The American Journal of ScienceJ.D. & E.S. Dana, 1913 - Earth sciences |
Contents
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Common terms and phrases
acid ægirite albite alkaline rocks analysis angle appear Ayahuaycco bands birefringence bones cadmium carbon Catskill cent chemical chloride color composition containing cristobalite crystals curve custerite Cuzco cycads deposits determined Devonian effect electrode equation eurypterid evidence fauna feet feldspar ferric oxide Fitch Hill flora fluoride formation fossils fusion Geol Geological given gneiss gram gravel gray heat igneous rocks ignition indicated inversion inversion-point ionization iron Kokomo lava limestone lower magma magnetic mass material metal method miles mineral Noblesville observed obtained occur optical origin Otozamites oxide oxygen pegmatites plant beds plate portion present Pterophyllum pyroxene quartz Quebrada radiation red shale region sand sandstone schists SCI.-FOURTH SERIES sediments shale shown silica sodium paratungstate sodium peroxide solar solution species specimens strata subalkaline sulphide sulphur surface Table telluric acid temperature thickness thin tion Titicaca tridymite upper vapor volts Williamsonia
Popular passages
Page 29 - ... pottery found along stream banks and which may have been deposited on terraces or on banks, or in the numerous small cave-like openings in the gravels, to be transported, buried, or reexposed during alternating processes of deposition and degradation. It is interesting to note that in the canyoned tributaries of the Sappi and of streams leading from the limestone plateau and from the...
Page 186 - ... Academy shall, whenever called upon by any Department of the Government, investigate, examine, experiment, and report upon any subject of science or art, the actual expense of such investigations, examinations, experiments, and reports to be paid from appropriations which may be made for the purpose, but the Academy shall receive no compensation whatever for any services to the Government of the United States.
Page 39 - ... and, as such, is frequently present in pneumatolytic minerals. As stated by Vogt, it seems to be more common in the acid rocks, but there seems to be a marked tendency on its part to favor especially rocks which are high in soda. This is seen in the fact that fluorite is frequently present as an original constituent of such highly sodic rocks as nephelite-syenite, phonolite, and tinguaite ; the association of fluorine and sodium in certain rare minerals, as leucophanite, meliphanite, johnstrupite,...
Page 439 - Cntch, an area of 10,000 square miles flooded by the sea for a part of the year, during the period of onshore monsoon winds. In the detection of mud-cracks in ancient formations, reasonable care must be used to avoid mistaking for them a polygonal cracking of the rock arising after its solidification. The two, however, are readily distinguished. True mud-cracks always have a filling, the polygons are irregular but do not show an irregularity constant in one direction.
Page 4 - Cuzco, while the canine bones may be referred to a dog. The site of the discovery of the bones of the " Cuzco man " was carefully examined, and Dr. Eaton states : After studying the form and composition of the walls of the quebrada and examining other deposits of bones both here and elsewhere in the Province of Cuzco, I am led to the opinion that the bones excavated in 1911 were not originally embedded in the basal gravel of the spur at the time when that gravel was itself in process of deposition,...
Page 29 - Professor Gregory's report (p. 29) throws -an entirely new light on the geological conditions in the Ayahuaycco gulch. He concludes : It is unprofitable, from a geological standpoint, to work out the details of erosional history in and about Cuzco. because of the extensive modification of slopes and terraces resulting from cultivation and flood-water irrigation. However, the evidence indicating periodic destruction and building of terraces, even within the past 100 years, removes the necessity of...
Page 383 - The inversion-temperatures under atmospheric pressure are 870° ± 10° quartz ^l^ tridymite 1470° ± 10° tridymite ^T± cristobalite. The velocity of transformation of one form of silica into another has been found to be very slow and in many cases the process follows Ostwald's rule ; that is, an unstable form does not pass directly into the most stable form, but the action progresses through successive steps, and intermediate phases appear, which eventually reach the stage of greatest stability....
Page 433 - The molluscan fauna of the Chemung and Catskill is unquestionably marine. Even the mollusks found in New York above the Oneonta sandstone belong to the ordinary forms. Of course it is possible, even probable, that at the extreme northeast there were small areas at the mouths of large rivers where fresh water prevailed and fresh-water mollusks lived ; but positive evidence of this is wanting.
Page 425 - Bulletin 535, 1913, 38 pp. A geologic reconnaissance of the Fairbanks quadrangle, Alaska, by LM Prindle, with a detailed description of the Fairbanks district, by LM Prindle and FJ Kutz, and an account of lode mining near Fairbanks, by PS Smith.
Page 384 - A study of the remarkable variations in the temperature of inversion of a- into /3-cristobalite has led to the conclusion that this mineral is made up of two different molecular species of silica within the same crystal. Various other properties of the silica minerals seem to have considerable bearing upon theories of the structure of molecules and crystals. The nature of the radical differences existing between the two different types of inversion has been discussed in some detail. The melting-point...