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| Keywords: The Quarterly journal of the Geological Society of London (13205728875).jpg 1846 SEDGWICK ON THE FOSSIL SLATES OF N WALES ETC 139 <br> appear here and there in the beds of this trough first breaking out <br> on the higher part of the brow ascending from the Penrhyn quarries <br> to Llyn Ogvven Along this line we have a Ibssiliferous zone about <br> half a mile wide and it ranges through the higher crests of Snowdon <br> to Moel Hebog as stated in former papers In many extensive <br> tracts it is true that fossils disappear especially where contempora- <br> neous porphyries and trappean shales are most abundant ; but the <br> whole series of undulations continued from the high crests here no- <br> ticed over the Berwyns and to the edge of Shropshire belong to <br> one great physical group the whole of which where the conditions <br> are favourable to the development of animal life is fossiliferous <br> Such are the sections from the Menai to the crests of the Car- <br> narvon chain ; and I cannot estimate the thickness of the beds be- <br> fore we reach the fossiliferous trough above noticed at less than six <br> or eight thousand feet <br> But there is one great imperfection in these sections ” they have <br> no well-defined base ; and we have no evidence on which to estimate <br> the thickness of deposits which may have been interpolated between <br> the hypozoic group and the dark earthy slates of Carnarvon and <br> Bangor Moreover it is almost impossible to form any correct esti- <br> mate of the thickness of the masses occupying the low country be- <br> tween the Menai and the western flank of the Carnarvon chain ; we <br> must therefore seek for better CN idence in other sections <br> Section III <br> Near Tremadoc <br> Horizontal distance 8 mUes – ' <br> S by W <br> a Lingulabeds <br> b Black slates with Fucoids and Trilobites <br> c Trilobites c <br> I have stated in my former papers that a great dislocated group of <br> slates and porphyries not to be mineralogically distinguished from <br> the general mass of the Carnarvon chain occupied the promontory <br> south of Tremadoc and was continued northward till it abutted <br> against the south flanks of Moel Hebog and Moel Ddu a few miles <br> south of Beddgelert ; but I had not seen this group since 1831 Its <br> beds first dip nearly north and then bending round toward the <br> western side of the great estuary called Traeth Mawr the beds dip <br> about N N E Before rising to the flanks of Moel Hebog and Moel <br> Ddu they reach a great elevation and become in some places almost <br> See Proceedings of the Geological Society vol iii p 548 36932868 113687 51125 Page 139 Text v 3 http //www biodiversitylibrary org/page/36932868 1847 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 3 1847 Geology Periodicals Smithsonian Libraries bhl page 36932868 dc identifier http //biodiversitylibrary org/page/36932868 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-17 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13205728875 2015-08-26 12 52 28 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1847 Photos uploaded from Flickr by Fæ using a script | ||||
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