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| Keywords: The Quarterly journal of the Geological Society of London (13205664785).jpg 1846 <br> SHARPE ON SLATY CLEAVAGE <br> 85 <br> are flattened and drawn out considerably in one direction without <br> the crumpling up or folding under of any part of the shell; as <br> in fig 14- representing a specimen of Spirifer giganteus restored <br> where the hinge had been broken off The pressure of the rock in <br> Fig 14 <br> A <br> JD <br> 3 if a noqii <br> foB ig h£iu y\ <br> £¥ – <br> the direction perpendicular to the cleavage has caused the flattening <br> of the shell and there has been an expansion of nearly 50 per cent <br> in another direction along the plane of cleavage Not having seen <br> this or any similar specimen in situ I could not learn the direction <br> of the line of elongation but there can be little doubt that it is par- <br> allel to the dip of the cleavage planes ; for in every other case the <br> elongating force has acted in a direction parallel to their dip not- <br> withstanding variations in the position of the bedding <br> Having examined all the principal cases of distortion in detail we <br> may take a broader view of the subject and consider them with re- <br> ference to the position of the shells in the bedding The beds of <br> slate vary much in thickness and are frequently separated by thin <br> layers of shells some of which are impressed on each of their surfaces <br> When we compare the fossils on the opposite sides of a bed of slate <br> we find them distorted along lines of which the direction is parallel; <br> but if there has been any oblique pressure it has acted in opposite <br> directions on the two sides of the bed This will be better under- <br> stood from fig 15 which represents the section of part of a thin bed <br> of slate at South Petherwin of which the lines A B a 5 are the upper <br> and lower surfaces each of which bears in relief flattened and dis- <br> torted casts of bivalve shells C D of which one side is seen the other <br> being buried in the slate; the cleavage Y Y is very oblique Be- <br> fore the slab was removed it rested of course upon a bed of rock <br> below and was covered bv another above which otFered resistance to 36932814 113687 51125 Page 85 Text v 3 http //www biodiversitylibrary org/page/36932814 1847 Geological Society of London NameFound Spirifer giganteus NameConfirmed Spirifer Martinia giganteus Caneva 1907 Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 3 1847 Geology Periodicals Smithsonian Libraries bhl page 36932814 dc identifier http //biodiversitylibrary org/page/36932814 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 N02/13205664785 2015-08-26 12 54 45 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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