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| Keywords: The Quarterly journal of the Geological Society of London (13936992701).jpg 1 02 PEOF T G BONNET ON TWO TEAVEESES OF THE <br> believe it and this agrees with the impression formed in the field <br> to have been a gneiss of the Laurentian type <br> 6 Gneiss 4 Ml West of La Grave p 75 ” The constituents are <br> as above described except that there is little or no epidote but a few <br> very small almost colourless garnets are present The mica how- <br> ever occurs in larger flakes and evidently is mostly biotite more or <br> less altered The structure of the rock has been modified by pressure <br> but the original one is retained more distinctly than in the former <br> case It is that of a very old gneiss not of a normal granite <br> c Gneiss from glen below the Meije Glacier p 77 ” The differ- <br> ences from the last described are only varietal <br> y Carboniferous Series near Le Freney <br> a Matrix of the Conglomerate east side of village p 74 ” This <br> is mainly composed of small fragments which are cemented by a <br> minutely flaky or granular material of paler dusty grey colour ; pro- <br> bably the latter largely consists of mica produced by the decompo- <br> sition of pulverized felspar Here and there is a fair-sized flake of <br> white mica The fragments occasionally contain felspars of fair size <br> about 05 long but the matrix of these and the whole of the rest <br> consists of a mottled mosaic of quartz apparently traversed by thin <br> wavy bands chiefly of the above-mentioned microscopic mica Their <br> structures suggest a derivation from a gneiss or schist that has been <br> greatly crushed and sheared As these structure-lines point in all <br> directions in the slide it is difficult to refer them to Post-Carbon- <br> iferous movements The neighbouring rock however when in its <br> normal conditions appears to be the ordinary coarse crystalline rock <br> described in Sect I It would seem therefore as if the fragments <br> had not been derived from the immediate vicinity and their struc- <br> ture was a record of Pre-Carboniferous disturbances <br> b The Slate west of the village p 73 consists of fragmental <br> quartz commonly very angular ; felspar more or less decomposed ; <br> white mica with rarely a little brown and tourmaline very rare <br> The rude cleavage- lines are darkened by the deposit of a carbonaceous <br> substance which is more or less disseminated throughout the slide <br> We have evidently here a rather fine detritus the fragments rarely <br> exceed -01 in diameter derived from a crystalline series The <br> mineral changes in the rock since Carboniferous times appear to me <br> to have been extremely slight yet as stated above p 73 it is com- <br> pletely infolded between huge masses of crystalline rock and must <br> have been affected by Pre-Jurassic as well as by Tertiary disturb- <br> ances <br> 3 Calc-mica-schists East of the Watershed of the Cottian Alps <br> pp 80-82 <br> As stated in the foregoing paper these rocks belong to one <br> general type the individual constituents being small grains or <br> flakes generally less than -01 in diameter except in the cases of <br> This is also true of the larger fragments 36939883 113696 51125 Page 100 Text 45 http //www biodiversitylibrary org/page/36939883 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 36939883 dc identifier http //biodiversitylibrary org/page/36939883 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 N02/13936992701 2015-08-26 06 55 31 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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