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| Keywords: The Quarterly journal of the Geological Society of London (14052725736).jpg EEV J HILL ON THE ROCKS OF GUERNSEY 409 <br> Fig 1 ” Grooved Weathering in Dioritic Hock a Quarter of a Mile <br> south of Fort Doyle <br> L <br> or 10 feet thick in the midst of coarsely crystalline rock dipping <br> about 50° or 60° to the N E visible on both sides of the headland <br> and running into the sea I thought at first that they passed con- <br> tinuously both above and below into the neighbouring crystalline <br> rock and that if they were sediraentary so must it be also But <br> doubts expressed by Professor Bonney after examining slides from <br> the rocks led me to make a more minute inspection than before I <br> had already noticed that the banded appearances were narrower and <br> less conspicuous on the western side of the point Investigating <br> this it appeared that some striping existed in the crystalline rock <br> itself I then saw that in places weathering developed this striping <br> till it bore a close resemblance to bedded structure Finally I was <br> able though with much difficulty to trace an actual line of division <br> between the slaty beds and the surrounding crystalline mass <br> With hesitation then I venture to suggest the following explana- <br> tion for this place The igneous rock has caught up or surrounded <br> a large slab of slaty beds and structures have been set up in the <br> igneous mass parallel to the surface of the slate These structures <br> weather into mock bedding and cause the appearance of a continuous <br> passage from normal igneous into normal stratified rock It is not <br> easy to be certain about the exact nature of these structures They <br> may perhaps be surfaces of crushing where the rock has yielded <br> along certain planes such as Prof Bonney has described in the <br> ' Geological Magazine ' 1883 p 436 Several yards to the south of <br> the slaty beds is a thin streak not an inch wide extending for many <br> feet which can scarcely be anything else a section cut from it is <br> described by Prof Bonney It seems to follow a joint and has a <br> horny texture which runs in wavy lines through the crystalline <br> syenite-like rock Other similar streaks I have noticed along the <br> northern shore <br> It is obvious from the shattered condition of the rocks of this <br> island that they have been subjected to enormous pressures Where <br> a rock under such pressures gives way along a plane and one surface <br> slides over the other the powder which the rock will be ground <br> into would probably resemble sedimentary material Heat would <br> be developed would this not assist in recementing it 36941228 113697 51125 Page 409 Text 40 http //www biodiversitylibrary org/page/36941228 1884 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 40 1884 Geology Periodicals Smithsonian Libraries bhl page 36941228 dc identifier http //biodiversitylibrary org/page/36941228 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 N02/14052725736 2015-08-26 05 51 17 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1884 Photos uploaded from Flickr by Fæ using a script | ||||
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