File:The Quarterly journal of the Geological Society of London (13937463002).jpg
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[edit]DescriptionThe Quarterly journal of the Geological Society of London (13937463002).jpg |
VICTORIA PARK, WHITEINCH, NEAR GLASGOW. 629 tionably belongs to the whin-vein, indicates that there is a difference in the chemical composition of the two bands, the deep colour of the glass in contact with the shale being probably due to the presence of metallic oxides in the latter rock. If this be so, the dark-colonred glass results from the fusion of the shale. It may be that this is merely the outermost glassy selvage of the whin -vein, tinted more or less by metallic oxides derived from a very slight in- cipient fusion of the shale. Assuming, for the moment, that this is the case, we have to account for the well-defined sinuous line of demarcation between the coloured and colourless bands of glass, and regarding these two bands as viscous matter of different densities, the existence of such a line, the trace of an undulating separation- surface, in a rapidly cooling magma is precisely what one would expect. A more perfect incorporation of the two glasses would have resulted in a lowering of tint and in the abolition of any such line of demarcation. The colourless glass may therefore be regarded as the tachylyte of the whin- vein, while the darker band I propose to distinguish by the term shale-glass. As already pointed out by Messrs. J. Young and D. Corse Glen, a considerable variation in texture and colour is met with in the material constituting the intrusive veins at Whiteinch, and, to quote their own words, " Where thinner sheets and veins derived from the main mass are found to be intrusive in higher or lower levels of the strata in the same locality, as in the quarry at Victoria Park, the rock is generally seen to pass from its normal dark colour into different shades of light grey and greyish white, the alteration being evidently due to its contact with the sedimentary rock and to rapid cooling, especially along the lines of contact " *. Mr. Young has kindly forwarded small specimens of the veins at Victoria Park, showing these variations, and I have examined sections made from those which appeared most typical, with the result that I find the dark, coarsely crystalline dolerite to consist of felspars which, from their extinction -angles, appear to be labradorite, but which are, for the most part, in too advanced a stage of alteration to admit of any optical determination. Olivine and ilmenite are also plentiful — the former mineral often showing alteration into serpentine or calcite, while the ilmenite has been, in great part, converted into leucoxene. Apatite is also plentiful in the form of slender hexagonal prisms. A considerable amount of green to brownish-green chlorite is also present, occasionally form- ing fringes, composed of fan-shaped aggregates of plates, around the walls of vesicles, the central portion of the vesicle being frequently filled with calcite. In addition to the minerals mentioned, the section shows a few small crystals of a dark-brown magnesian mica, and here and there a speck of pyrites. Another specimen from the same locality, but of a totally different character from the preceding, is very fine-grained in texture, and of a pale bluish-grey, passing into a buff colour. In a section taken Trans. Geol. Soc. Glasgow,1888. |
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Source | https://www.flickr.com/photos/biodivlibrary/13937463002 | ||
Author | Geological Society of London | ||
Full title InfoField | The Quarterly journal of the Geological Society of London. | ||
Page ID InfoField | 36940474 | ||
Item ID InfoField | 113696 (Find related Wikimedia Commons images) | ||
Title ID InfoField | 51125 | ||
Page numbers InfoField | Page 627 | ||
BHL Page URL InfoField | https://www.biodiversitylibrary.org/page/36940474 | ||
Page type InfoField | Text | ||
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Flickr posted date InfoField | 21 April 2014 | ||
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26 August 2015
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current | 05:35, 26 August 2015 | 1,166 × 2,096 (530 KB) | Fæ (talk | contribs) | == {{int:filedesc}} == {{BHL | title = The Quarterly journal of the Geological Society of London. | source = http://www.flickr.com/photos/biodivlibrary/13937463002 | description = VICTORIA PARK, WHITEINCH, NEAR GLASGOW. 629 <br> tiona... |
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