MAKE A MEME View Large Image The Quarterly journal of the Geological Society of London (13205684005).jpg 1846 SHARPE ON SLATY CLEAVAGE 99 <br> when the heated mass cooled and a contraction took place in con- <br> sequence <br> The undulating surface of the cleavage ...
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Keywords: The Quarterly journal of the Geological Society of London (13205684005).jpg 1846 SHARPE ON SLATY CLEAVAGE 99 <br> when the heated mass cooled and a contraction took place in con- <br> sequence <br> The undulating surface of the cleavage over the central parts of <br> Devonshire in low waves which either coincide with more boldly <br> arched waves of the bedding the two having a common axis parallel <br> to the boundaries of the area or which cut obliquely through the <br> curves of the bedding is a phsenomenon which requires for its <br> explanation the depression of the centre of the area after the forma- <br> tion of the cleavage The elevation of the bedding in folds parallel <br> to the axis might be regarded as part of the original movement; but <br> not so the undulations of the cleavage ; and the peculiarity that the <br> waves of the bedding and cleavage sometimes coincide in direction <br> and sometimes differ refers them to two operations of which the <br> cleavage being the less disturbed seems only to have undergone the <br> later one This undulation of the cleavage has only been noticed <br> over the centre of the flat arch of elevation of Devonshire in di- <br> stricts where the beds and the cleavage planes are tilted at considera- <br> able angles a lowering of the arch might have taken place which <br> it would be difficult to detect <br> The foreign crystalline matter which is frequently found between <br> the planes of cleavage shows that at some period after the cleavage <br> was completed the rock had a tendency to gape along them Mr <br> Darwin has collected many instances of the kind from his own ob- <br> servations and those of Professor Sedgwick of which the most re- <br> markable is the occurrence of trap dikes in Tierra del Fuego between <br> the laminae of the slates f <br> In the cliffs at the foot of Hillsborough and in other places near <br> Ilfracombe many instances may be seen of the insertion of sheets of <br> quartz between the laminae of slate as shown in the section fig 21 <br> Fig 21 <br> XXKSX <br> The horizontal lines represent the beds the oblique dotted lines the cleavage and the thick black <br> lines the sheets of quartz <br> The quartz which is often an inch thick lies partly between the beds <br> Darwin Geological Observations on South America pp 152 160 and 163 <br> Sedgwick Transactions of the Geological Society 2nd Series vol iii p 471 <br> + Had I been aware of this observation 1 should have sought for similar phae- <br> nomena among the greenstone dikes of Carnarvonshire which strike with the <br> cleavage and bedding of the district but of which the dip has not been satisfactorily <br> ascertained <br> H 2 36932828 113687 51125 Page 99 Text v 3 http //www biodiversitylibrary org/page/36932828 1847 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 3 1847 Geology Periodicals Smithsonian Libraries bhl page 36932828 dc identifier http //biodiversitylibrary org/page/36932828 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-17 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13205684005 2015-08-26 12 55 13 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1847 Photos uploaded from Flickr by Fæ using a script
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