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| Keywords: The Quarterly journal of the Geological Society of London (12893450595).jpg 216 <br> MR W P D STEBBING ON TWO BOULDERS OF May 1 897 <br> grains of a mineral having a very slight earth -brown tint in <br> ordinary light and appearing with crossed nicols as an aggregate <br> of minute specks inclining to flaky or fibrous which bave weak <br> depolarizing power probably a pinite after cordierite A very <br> little of rather altered biotite and iron oxide also zircon and <br> rutile both small and rare The structure of the rock is not that <br> of a normal granite but more nearly resembles one of those which <br> are often banded and commonly occur in a complex of the older <br> Archaean such as the so-called Laurentian or Hebridean see ng 1 <br> 'Boulder B ” The constituents in this specimen differ in that much <br> of the felspar is ordinary plagioclase and orthoclase is more certainly <br> present the pinitic mineral is doubtfully present; there is very <br> Fig 1 ” Microscopic section of Boulder A <br> X30 <br> The dark grain at the edge about S S W of the centre is blackened biotite <br> and there are some small films to the N W of it The lighter grains are <br> quartz ; the rest is felspar A trace of minute micrographic structure is <br> visible The rock is cracked but the peculiarly formed clear space <br> between S E and E S E is caused by a breakage in the slice <br> little biotite but much white mica A little of this may be <br> bleached biotite and in one or two cases I think that small flakes <br> of biotite are interlaminated There is a small elongated cluster <br> of impure red garnets pierced longitudinally by a thin tongue of <br> quartz see fig 2 In this rock signs of mechanical action are <br> clear The mica is sometimes bent or 'rucked ' the quartz and 36028993 111130 51125 Page 216 Text 53 http //www biodiversitylibrary org/page/36028993 1897 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 53 1897 Geology Periodicals Smithsonian Libraries bhl page 36028993 dc identifier http //biodiversitylibrary org/page/36028993 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-03 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12893450595 2015-08-26 17 55 17 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1897 Photos uploaded from Flickr by Fæ using a script | ||||
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