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| Keywords: The Quarterly journal of the Geological Society of London (13937463002).jpg VICTORIA PARK WHITEINCH NEAR GLASGOW 629 <br> tionably belongs to the whin-vein indicates that there is a difference <br> in the chemical composition of the two bands the deep colour of the <br> glass in contact with the shale being probably due to the presence of <br> metallic oxides in the latter rock If this be so the dark-colonred <br> glass results from the fusion of the shale It may be that this <br> is merely the outermost glassy selvage of the whin -vein tinted <br> more or less by metallic oxides derived from a very slight in- <br> cipient fusion of the shale Assuming for the moment that this <br> is the case we have to account for the well-defined sinuous line of <br> demarcation between the coloured and colourless bands of glass and <br> regarding these two bands as viscous matter of different densities <br> the existence of such a line the trace of an undulating separation- <br> surface in a rapidly cooling magma is precisely what one would <br> expect A more perfect incorporation of the two glasses would have <br> resulted in a lowering of tint and in the abolition of any such line <br> of demarcation The colourless glass may therefore be regarded <br> as the tachylyte of the whin- vein while the darker band I propose <br> to distinguish by the term shale-glass <br> As already pointed out by Messrs J Young and D Corse Glen <br> a considerable variation in texture and colour is met with in the <br> material constituting the intrusive veins at Whiteinch and to quote <br> their own words Where thinner sheets and veins derived from the <br> main mass are found to be intrusive in higher or lower levels of the <br> strata in the same locality as in the quarry at Victoria Park the <br> rock is generally seen to pass from its normal dark colour into <br> different shades of light grey and greyish white the alteration being <br> evidently due to its contact with the sedimentary rock and to rapid <br> cooling especially along the lines of contact <br> Mr Young has kindly forwarded small specimens of the veins at <br> Victoria Park showing these variations and I have examined <br> sections made from those which appeared most typical with the <br> result that I find the dark coarsely crystalline dolerite to consist of <br> felspars which from their extinction -angles appear to be labradorite <br> but which are for the most part in too advanced a stage of <br> alteration to admit of any optical determination Olivine and <br> ilmenite are also plentiful ” the former mineral often showing <br> alteration into serpentine or calcite while the ilmenite has been in <br> great part converted into leucoxene Apatite is also plentiful in <br> the form of slender hexagonal prisms A considerable amount of <br> green to brownish-green chlorite is also present occasionally form- <br> ing fringes composed of fan-shaped aggregates of plates around the <br> walls of vesicles the central portion of the vesicle being frequently <br> filled with calcite In addition to the minerals mentioned the <br> section shows a few small crystals of a dark-brown magnesian mica <br> and here and there a speck of pyrites <br> Another specimen from the same locality but of a totally different <br> character from the preceding is very fine-grained in texture and of <br> a pale bluish-grey passing into a buff colour In a section taken <br> Trans Geol Soc Glasgow 1888 36940474 113696 51125 Page 627 Text 45 http //www biodiversitylibrary org/page/36940474 1889 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 45 1889 Geology Periodicals Smithsonian Libraries bhl page 36940474 dc identifier http //biodiversitylibrary org/page/36940474 smithsonian libraries Information field Flickr posted date ISOdate 2014-04-21 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13937463002 2015-08-26 05 52 10 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1889 Photos uploaded from Flickr by Fæ using a script | ||||
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