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| Keywords: The Quarterly journal of the Geological Society of London (12711464723).jpg 1854 <br> SHARPE ” STRUCTURE OF MONT BLANC <br> 21 <br> of one great operation of which we must carefully study the effects <br> before we can hope to learn its causes or nature <br> Let us now turn to the line of valleys which under the names of <br> the Allee Blanche and the Val Ferret bounds the eastern side of the <br> Mont Blanc range The western side of the Alle'e Blanche is in a <br> great measure masked by the enormous moraines of the great glaciers <br> which descend from Mont Blanc and the various interesting phseno- <br> mena connected with these somewhat distracted my attention from <br> the geology of the valley ; but I sketched the section shown in <br> fig 2 on the west or Mont Blanc side of the valley a little above <br> Fig 2 <br> Slaty limestone <br> Slate <br> Calcareous <br> conglomerate <br> Slate <br> 90 85° 80 70 <br> the Lac de Combal Slates of various characters rest conformably <br> on a bed of calcareous conglomerate in which the cleavage is very <br> obscure ; this rests on a thick formation of slaty limestone with <br> mica lying on the planes of cleavage The beds all dip conformably <br> to the S E at about the angle of 20° and are consequently resting <br> upon the gneiss of Mont Blanc The cleavage strikes N 25° E <br> dipping near the mountain towards the E 25° S at high angles but <br> is vertical in the limestone at the side of the valley ; this is on the <br> line of the western axis of vertical foliation of the gneiss of Mont <br> Blanc and connects that line with the vertical cleavage of the Col de <br> la Seigne These beds doubtless belong to the Jurassic series of the <br> Col du Bonhomme and may owe their more metamorphic character <br> to their proximity to the gneiss ; they cross the valley near the <br> chapel ; they are probably separated from the gneiss by a metamor- <br> phic siliceous slate which is seen on the west side of the valley below <br> the Glacier de 1' Allee Blanche <br> I examined the Piedmontese Val Ferret rather more in detail ; the <br> position of the rocks on the north side of the Col Ferret is shown in <br> Sect 3 PI I A thick bed of quartz rock rests upon the gneiss at <br> Saussure § 845 mentions two pyramidal hills of a similar micaceous lime- <br> stone near the head of the Allee Blanche with highly inclined beds ; he doubtless <br> mistook the cleavage planes for the stratification 35614579 110213 51125 Page 21 Text v 11 http //www biodiversitylibrary org/page/35614579 1855 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 11 1855 Geology Periodicals Smithsonian Libraries bhl page 35614579 dc identifier http //biodiversitylibrary org/page/35614579 smithsonian libraries Information field Flickr posted date ISOdate 2014-02-23 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12711464723 2015-08-26 20 56 27 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1855 Photos uploaded from Flickr by Fæ using a script | ||||
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