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| Keywords: The Quarterly journal of the Geological Society of London (13937264501).jpg ALDERNEY AND THE CASQJJETS 383 <br> granite and the normal darker rock may be seen sharply defined in <br> the bay south of JBibette Head <br> A granite similar to the pink decomposing form of this occurs in <br> outcrops on the southern cliffs ; as for instance on a slope north of <br> the islet called Coque Lihou where a pink and a bluish rock may be <br> seen in intrusive contact Some of this pink rock recalls the L'Eree <br> gneiss in Guernsey and itself shows under the microscope signs of <br> disturbance A specimen collected from somewhere on these cliffs <br> of this circle shows a very large orthoclase crystal of an inch long <br> such as characterizes the granite of Cap La Hague on the neigh- <br> bouring coast of France ; such crystals also characterize a rock at <br> L'Eree The perpendicular cliffs of this coast even more inaccessible <br> than those of Sark swept at their base by some of the most violent <br> tides in Europe offer serious obstacles to examination <br> The only locality where I have noticed crush-structure on a scale <br> visible to the eye is on the shore under Eort Tourgis Here are <br> seen many dark node-like patches some narrow and lenticular and <br> of these the axes lie with a certain amount of parallelism while the <br> rock itself has a rude appearance of a structure which is directed <br> N E to S W and vertical <br> The general appearance of the normal Alderney rock recalls the <br> diorites and syenites of Guernsey and some specimens can scarcely <br> be distinguished from some of the quartzose varieties of that group <br> But the abundance of mica and the smaller amount of hornblende <br> would connect it rather with the granites of Jethou and Sark The <br> microscopic study has resulted in a similar opinion <br> 3 Minor Igneous Rocks <br> The minor intrusive rocks of Alderney do not equal in interest <br> and variety those of Guernsey still less do they rival the singu- <br> larities which Jersey presents Nevertheless they are numerous <br> and interesting Most of the families found in the other islands <br> are represented Granites occur here and there one for instance <br> about a yard thick in the sides of a chasm in the crags north of <br> Port Albert Pink micro-crystalline quartz-felspar dykes are most <br> abundant ; the western headlands are cut by many so parallel that <br> an observer from a boat might even think the rock stratified and <br> so abundant that I estimated them to occupy more than one tenth <br> of the cliff-face They appear to be identical with the Guernsey <br> quartz-felspar dykes Quart Journ Geol Soc vol xl p 416 <br> Compacter pink dykes occur from Braye Harbour westwards <br> which may represent the pink felsites of Guernsey A remarkable <br> purple intrusion several feet thick may be followed some hundreds <br> of feet along the shore west of the causeway leading to Eort Clonque <br> and ultimately appears to transform itself into a variety of the last- <br> named group Under the microscope this shows a very compact <br> matrix speckled with opacite and containing small crystals of <br> felspar The matrix exhibits a minute devitrification and the rock <br> might perhaps be called a porphyrite Basic intrusions are less 36940202 113696 51125 Page 381 Text 45 http //www biodiversitylibrary org/page/36940202 1889 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 45 1889 Geology Periodicals Smithsonian Libraries bhl page 36940202 dc identifier http //biodiversitylibrary org/page/36940202 smithsonian libraries Information field Flickr posted date ISOdate 2014-04-21 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13937264501 2015-08-26 05 54 44 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1889 Photos uploaded from Flickr by Fæ using a script | ||||
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