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| Keywords: The Quarterly journal of the Geological Society of London (13936949831).jpg 72 PEOF T G BONNET ON TWO TEAVEESES OF THE <br> After this a more micaceous and banded rock is seen in situ <br> West of Livet comes a fairly strong mica-schist containing many tiny <br> garnets and traversed by numerous quartz- veins Appendix p 101 <br> In it cleavage-foliation has been developed at an angle of about 70° <br> with the horizon without however materially interfering with the <br> cohesion of the mass It is later in date than these veins for they <br> have been bent into serpentine curves which are thickened at the <br> crests of folds and attenuated at the sides just like bands of sand <br> in clay under pressure illustrating in a very interesting way the <br> principle of solution and deposition indicated by Dr Sorby <br> Beyond this place the crags recede from the road as the Combe de <br> Gavet opens out ; but the great infold of Jurassic rock out of which <br> has been excavated the singular plain around the confluence of the <br> Olle and the Yeneon with the Eomanche affords a wonderful spec- <br> tacle The strata here are very distinctly bedded not unlike parts <br> of the Lower Lias of England and thus by structure as well as <br> tint are distinguished at a glance from the underlying crystalline <br> masses Cleavage is well defined and is not far from the vertical ; <br> it cuts the bedding at various but generally high angles because <br> that structure not unfrequently is almost horizontal <br> /3 Bourg d'Oisans to Le Dauphin Grandes-Bousses Range fig 1 <br> Eoughly to the north of Bourg d'Oisans the crystalline rock reap- <br> pears from beneath the stratified On the south side of the valley <br> the former rises sharply up from beneath the latter to form a peak <br> perhaps 8000 feet above the sea ; on the north side an epaulette <br> of the latter rests on a kind of shoulder of the former so that the <br> peaks of the Grandes Bousses are almost enclosed by the Mesozoic <br> rocks North of the town a small mountain-road gives a good <br> opportunity of studying the relations of the two series for it zigzags <br> over their junction which however is only perfectly exposed in <br> one or two places <br> The crystalline rock is a rather fine-grained and somewhat massive <br> gneiss exhibiting distinct light and dark bands which are often <br> about inch thick It is not fissile for it breaks readily across <br> this structure which has a strike between NJN W and N W and a <br> dip of from 75° to 80° on the eastern side Microscopic examination <br> Appendix p 101 indicates that the rock after crystallization <br> has been modified by presssure ; but I am very doubtful whether the <br> banded structure can be attributed to this and think that the rock <br> when thus affected must have been already a banded gneiss re- <br> sembling those of the Laurentian series The base of the Jurassic <br> series is a hard quartzose grit which has apparently derived its <br> materials from the underlying rock Here and there it becomes <br> conglomeratic the fragments seeming to be identical with the <br> underlying gneiss <br> About two miles from Bourg d'Oisans the Eomanche issues from <br> a narrow gorge ; the valley of the Yeneon which drains the interior <br> of the great horseshoe of high peaks forming the massif of the High- 36939853 113696 51125 Page 70 Text 45 http //www biodiversitylibrary org/page/36939853 1889 Geological Society of London NameFound Combe NameConfirmed COMBE EOLID 12397 NameBankID 4122786 Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 45 1889 Geology Periodicals Smithsonian Libraries bhl page 36939853 dc identifier http //biodiversitylibrary org/page/36939853 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 N02/13936949831 2015-08-26 06 51 09 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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