Records of the Geological Survey of India, Volume 58

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The Survey, 1926 - Earthquakes
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Includes the "Annual report of the Geological Survey of India," 1867-
 

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Page 386 - Biotite is present in many sections of the gabbro, though not in all. It not only occurs in the neighborhood of magnetite, where this mineral is in contact with plagioclase, but it is sometimes found imbedded in the feldspar and augite, and at other times it forms a mosaic with decomposed diallage. In basal sections it is reddish brown, and in longitudinal sections is light yellow normal to the cleavage, and dark brownish-green, almost opaque, parallel to this structural feature. In all cases it...
Page 117 - Treated generally, palagonite may perhaps be regarded as a hydrous glassy substance of variable composition formed partly by hydration of the primary glass and partly at the expense of augite (? again largely hydration) and iron-ore, and with much more difficulty at the expense of felspar (? by replacement). In colour it ranges through orange and brown to brownish green and bright green, and the material of all colours may become ' devitrified ' and anisotropic in spherulites and concentric-radiate...
Page 197 - ... In the light of European experience, where most of our petrographical data have been established, the peculiarities of the Madras rocks call for some special consideration, and the object of this paper is to suggest that the probable explanation of the peculiarities now ' referred to arises from a contrast of the geological histories of the two areas. In Europe all, or nearly all, the rocks have been submerged below the sea during the later geological periods ; in South India there is no evidence...
Page 388 - In polarised light, these grains are seen not to be parts ot one large crystal, but to have very different orientations. The form of the individuals of pyroxene and olivine at once recalls the structure seen in granulites.
Page 365 - Broach, but these dips are believed to be due to the effects of late disturbances of level due to tectonic causes rather than to an original inclination of the flows.1 Petrology. In petrological composition the Deccan basalts are singularly uniform. The most common rock is a normal augitebasalt, of mean specific gravity 2'82. This rock persists, quite undifferentiated in composition, from one extremity of the trap area to the other. The only variation is in the colour and texture of the rock ; the...
Page 197 - ... the numerous occurrences of dunite throughout the Madras Presidency serpentine is extremely scarce. In a nepheline syenite recently discovered in the Coimbatore district, and at least of Cuddapah age, the nepheline on microscopic examination shows mere traces of alteration along the fracture cracks. In the light of European experience, where most of our petrographical data have been established, the peculiarities of the Madras rocks call for some special consideration, and the object of this...
Page 67 - Provisional list of Palaeozoic and Mesozoic Fossils collected by Dr. Coggin Brown in Yunnan.
Page 361 - ... surrounding ridges, give rise to four distinct areas of drainage, each discharging through one of the four gorges, in the outer ranges. This central pile, which is far loftier than the surrounding ridges (save that to the south, whose highest point nearly rivals...
Page 392 - Augite is also very abundant in the more holocrystalline types but becomes less so as the glass content increases and seems to be quite absent...
Page 365 - ... few, especially those of trachytic or more acid composition, are even of a rich brown or buff colour ; less common are red and purple tints. The texture varies from a fine-textured crypto-crystalline, almost vitreous anamesite, through all gradations of coarseness, to a coarsely crystalline dolerile.

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