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| Keywords: The Quarterly journal of the Geological Society of London (14096462793).jpg SCHISTOSE ROCKS OF NORTHERN DONEGAL <br> 223 <br> Donegal 'The revelation made by the rocks themselves was both a <br> surprise and a disappointment I have visited Prof Hull's most <br> critical sections and some districts not described by him <br> Pig 1 ” Section in Bar <br> Gap and on Lough Greenan <br> S E <br> Lough G-reenan Lough Salt <br> I <br> I <br> G Granite <br> L Limestone <br> Ms Mica-scliist <br> Hs Hornblende-schist <br> Section in Barnesheg Gap fig 1 north-west end <br> It was in this wild ravine near a wooden barrack erected for a <br> body of soldiers appointed to protect a cottage opposite that I fi rst <br> touched the granite The rock surfaces on each side were well <br> rounded by ice-action and the colouring and weathering suggested <br> some bits of Hebridean scenery in Scotland The first blow of the <br> hammer destroyed my preconceptions The rock was grey in colour <br> uniform in texture consisting of a well-crystallized coarse-grained <br> aggregate of quartz black mica and felspar mostly orthoclase <br> There were no signs of bedding and but for a roughly linear <br> arrangement of the mica I should have declared I had before me as <br> typical a granite as I had ever seen <br> Towards the junction with the schists at the south-eastern end <br> of the Gap the granite grows lighter in colour and less coarse in <br> grain At the entrance of the gorge we reach the important part <br> of the section Masses of schist lie between masses of granite and <br> at a hasty glance the two appear to be interstratified I first came <br> upon a thin band of well-crystallized mica-schist dipping at a <br> moderate angle to the south-east with granite on both sides of it <br> A little further on I reached hornblende-schist the hornblende <br> consisting of small black sparkling crystals predominating over the <br> quartz This rock at first was rather puzzling It had no regular <br> dip but rose vertically like a dyke with irregular sides as if it <br> had thickened abruptly downwards But this diorite-like mass was <br> distinctly foliated and I at first thought that I had before me a <br> case of pressure-foliation in an igneous rock The foliation how- <br> ever was not parallel to either of the margins of the mass or at <br> right angles to the direction of the thrust which had contorted <br> the region but sloped at a medium angle to the south-east in <br> accordance with the prevailing dip of the schists outside the granite <br> r2 37047075 114009 51125 Page 223 Text 41 http //www biodiversitylibrary org/page/37047075 1885 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 41 1885 Geology Periodicals Smithsonian Libraries bhl page 37047075 dc identifier http //biodiversitylibrary org/page/37047075 smithsonian libraries Information field Flickr posted date ISOdate 2014-04-30 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/14096462793 2015-08-26 04 51 54 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1885 Photos uploaded from Flickr by Fæ using a script | ||||
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