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| Keywords: The Quarterly journal of the Geological Society of London (12893678443).jpg 354 <br> DE C CALLAWAY ON THE OKIGLN OF <br> Aug 1897 <br> parallel with the foliation are several veins of grey fine-grained <br> rock some of which are a kind of halleflinta while others are <br> foliated They range in breadth from several inches to less than a <br> line Some of the thicker veins show a gradation within an inch <br> or so between halleflinta and gneiss Similar veins appear in the <br> floor of the quarry and strike across the road sometimes branching <br> They thin out to a point It is incredible that this grey rock should <br> be sedimentary and it is almost equally difficult to believe that it <br> can be older than the diorite in which it is enclosed <br> Fig 1 ” Gneiss of primary injection Llanyaffo <br> w - _______ E- <br> In thin sections some of the felsite or halleflinta exhibits the <br> minutely-granulated structure of the grey veins at Llangaffo ; but <br> it contains numerous granules of epidote the effect perhaps of <br> the chemical action of the enclosing diorite Junction-specimens <br> show this felsite to be interlaminated with bright clear horn- <br> blende whether by veining or infiltration I cannot say and <br> sometimes we observe the hornblende to alternate with fresh clear <br> plagioclase in long prisms lying in different directions It would <br> thus appear that in this locality there has been an actual fusion of <br> some of the constituents resulting not only in the generation of <br> new minerals but in the regeneration of the hornblende <br> Turning into the field close at hand we come to the typical <br> section p 356 of felsite graduating into grey gneiss and we are <br> thus led to infer that the veins in the road proceed from the same <br> Section at Forth Gwyfen <br> On the shore at this locality there is a very clear exposure of a <br> striped gneiss similar to the section shown in fig 1 Grey gneiss <br> and dark-green schist run into each other in numerous thin bands <br> The gneiss passes in places into halleflinta and veins of the grey <br> rock in the form of either halleflinta or gneiss are also seen in the <br> green schist at a distance from the junction of the two rocks In an <br> easterly direction the grey veins come in more and more abundantly <br> till we reach a large mass of grey gneiss 36029163 111130 51125 Page 354 Text 53 http //www biodiversitylibrary org/page/36029163 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 36029163 dc identifier http //biodiversitylibrary org/page/36029163 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 N02/12893678443 2015-08-26 17 53 50 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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