MAKE A MEME View Large Image The Quarterly journal of the Geological Society of London (14053368306).jpg ASSOCIATED KOCKS OF THE BKEIDDEX HILLS 545 <br> this one Where thrust in thin dykes into the shales large felspars <br> are still visible but they are set in a ...
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Keywords: The Quarterly journal of the Geological Society of London (14053368306).jpg ASSOCIATED KOCKS OF THE BKEIDDEX HILLS 545 <br> this one Where thrust in thin dykes into the shales large felspars <br> are still visible but they are set in a microcrystalline matrix com- <br> posed of small felspar crystals and calcite which latter has taken the <br> place of all but the felspar and even attacked that This rock is <br> either an eustatite or olivine diabase <br> These rocks are all intrusive into the Criggion shales surrounding <br> them and evidence of this is abundant throughout the district On a <br> small branch of Belleisle Brook the subjoined section fig 5 shows the <br> Fig 5 ” Section in small trihutary of Belleisle Brook <br> Length 15 feet <br> D Diabase intrusive in shale S' <br> S Fragment of shale caught in diabase <br> intrusion of diabase and at least two other distinct veins of it have <br> been found in other parts of this brook and its tributaries connecting <br> the Brimford Wood with the northern massifs Then again the <br> actual contact is seen to the west of the Criggan where the diabase <br> alters the shales very considerably at contact A thin section of <br> shale taken from this spot shows a development of small scales of <br> white mica and of greenish brown dichroic mica parallel to the <br> lamination ; but the most interesting feature is the incipient breccia- <br> tion of the rock by a number of minute faults evidently caused by <br> the violence of intrusion The faults vary in throw from -2 to -03 <br> inch and some of the very smallest may be as little as '006 inch in <br> throw ; most of them are normal but the largest and a few others <br> are reversed ” I count 14 of them in a specimen 2 inches long On <br> the S E side similar hardening takes place the shales often being <br> burnt red ; but I cannot recognize any secondary crystallization At <br> Trewem and round Eodney's Pillar Hill the shales are also much <br> contorted and hardened near the junction ; in the quarry near But- <br> tington station sand-beds are converted into quartzite <br> As to the age of the diabases we cannot do much more than con- <br> jecture In no place do they actually traverse Silurian rocks but <br> near Buttington the later rocks are as remarkably distui bed as the <br> Cambrian and I trace this disturbance to the intrusion of igneous rock <br> If they are really post-Silurian it is very difficult to assign their <br> exact age ; for in this part of the country most of the post-Silurian <br> igneous rocks are later than early Carboniferous and are dolerites <br> much less altered than these and with a different mineral composition <br> and structure It is of course possible that they may belong to the <br> 2q2 37047425 114009 51125 Page 545 Text 41 http //www biodiversitylibrary org/page/37047425 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 37047425 dc identifier http //biodiversitylibrary org/page/37047425 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 N02/14053368306 2015-08-26 04 55 21 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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