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| Keywords: The Quarterly journal of the Geological Society of London (12511796355).jpg 88 PROCEEDINGS OF THE GEOLOGICAL SOCIETY Feb 23 <br> bright green in well-defined layers It contains very numerous <br> nodules or fragments chiefly of white translucent quartz varying <br> from the size of a pin's head to that of a horse-bean These are <br> cemented by a calcareous opaque friable matrix On the west bank <br> below the bridge this sandstone has both imbedded in it and resting <br> on the naked gneiss large boulders of the same gneiss � some weigh- <br> ing many hundred weight One of these Sir Charles Lyell found by <br> admeasurement to be 8 feet long <br> When the water is low an interesting fact is seen near the east <br> bank 350 yards above the bridge On the prolonged flank of a <br> mound of gneiss rest some horizontal layers of Potsdam sandstone <br> They gradually thin ofi as they ascend the mound and cease see <br> fig 1 but the superincumbent hmestone is continued and in im- <br> mediate contact with the gneiss mound covers its little crest and its <br> opposite side <br> Fig 2 � Section showing the superposition of beds of Potsdam sand- <br> stone and Trenton limestone on gneiss River Montmorenci <br> a Gneiss h Potsdam sandstone e Trenton limestone <br> The Potsdam sandstone at this place has not yet been found to <br> contain organic remains <br> The Trenton limestone which reposes conformably on the Potsdam <br> sandstone is amply displayed It constitutes the whole mural gulley <br> at the Natural Steps and lines both banks of the river either in slopes <br> or clifi's from thence to the brink of the great Falls On the west <br> side of the brink the clifi is 40 feet high chiefly consisting of Trenton <br> limestone with the rocks beneath well exposed <br> The Trenton limestone at Montmorenci is fetid moderately hard <br> finely granular black bluish or blackish brown Certain thin <br> layers at every level are abruptly crystalline and pale brown ; others <br> again take on a quasi-conglomerate appearance with rounded con- <br> cretions from the size of an orange downwards At irregular intervals <br> a dark calcareous shale from 6 to 18 inches thick is intercalated; <br> and this as we shall find is soon under the name of Utica slate <br> wholly substituted for the Trenton rock <br> The sides of the clifi over which the Montmorenci plunges into <br> the River St Lawrence show the manner in which the Trenton lime- <br> stone passes into the next and upper division of Silurian rocks Utica <br> slate represented in Wales by Llandeilo flags and the Hudson <br> River group ; and it is thus � on both sides of the chasm the middle <br> being wholly of gneiss the Trenton limestone becomes rapidly both 34983191 108767 51125 Page 88 Text v 9 http //www biodiversitylibrary org/page/34983191 1853 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 9 1853 Geology Periodicals Smithsonian Libraries bhl page 34983191 dc identifier http //biodiversitylibrary org/page/34983191 smithsonian libraries Information field Flickr posted date ISOdate 2014-02-14 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12511796355 2015-08-27 09 56 47 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1853 Photos uploaded from Flickr by Fæ using a script Potsdam Sandstone | ||||
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