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| Keywords: The Quarterly journal of the Geological Society of London (12960401793).jpg ANNIVEESAET ADDEESS OP THE PEESIDElfT 89 <br> slate from Wicca Pool altered into fine-grained schist However <br> as in some of the specimens from Wicca Pool there has sometimes <br> been little or no horizontal segregation and the bands of different <br> mineral composition are continuous like small deposited beds ; but <br> frequently some of these are so exclusively quartzose and others <br> so exclusively micaceous that I think the original differences due <br> to stratification must have been greatly increased by vertical segre- <br> gation Even when this kind of evidence is wanting the mutual <br> arrangement of the constituent crystals clearly shows that their <br> present outline is due to growth in situ A portion of a spe- <br> cimen from Loch Groyle magnified 60 linear shown by fig 10 <br> Pig 10 ” Mica-schist of Loch Goyle with stratification-foliation <br> 3 \ <br> will serve to illustrate some of the more important facts At the <br> bottom we have a layer containing much mica and in the centre <br> one composed more exclusively of quartz In this layer lie large <br> and smaller plates of mica enclosed in a number of interfering <br> crystals of quartz which have obviously crystallized in situ round <br> them and about them Similarly when we examine the micaceous <br> layer we may see that the crystals of mica also mutually interfere <br> and enclose quartz so that the proof of crystallization in situ is <br> equally good <br> It is however in the case of cleavage-foliation that the proof of <br> recrystallization is the most complete ; and since the great impor- <br> tance of this structure appears to be often overlooked it will be <br> well to consider it somewhat in detail <br> By far the best district that I have seen for studying this kind <br> of foliation is that ly'mg along the sea-coast between Aberdeen <br> and Stonehaven especially at Portlethon Muchals and Skateraw <br> At Muchals I obtained specimens which are remarkably instructive <br> because they show in the same thin section both stratification- <br> foliation and cleavage-foHation Pirst of all we may see bands of <br> different mineral character showing stratification as clearly as any <br> slate but necessarily modified by a variable amount of horizontal <br> and vertical segregation Eoughly parallel to these thin beds lie <br> VOL XXXVI i 36091176 111264 51125 Page 89 Text 36 http //www biodiversitylibrary org/page/36091176 1880 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 36 1880 Geology Periodicals Smithsonian Libraries bhl page 36091176 dc identifier http //biodiversitylibrary org/page/36091176 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-06 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12960401793 2015-08-26 15 55 52 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1880 Photos uploaded from Flickr by Fæ using a script | ||||
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