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| Keywords: The Quarterly journal of the Geological Society of London (13204715765).jpg PEE-CAMBRIAN EOCKS OF ST DAVID S <br> 287 <br> Fig 7 Contemporaneous Erosion accompanying Cambrian <br> Conglomerates Caer-fai St David's <br> the coast-section or looking at the occasional exposures inland <br> and finding that all the tuffs breccias and diabase sheets dip <br> steadily in a north-westerly direction would infer that he is <br> crossing a continuous succession of beds the highest being at the <br> north-west end and the lowest at the south-east end of the section <br> This natural inference has been drawn by Dr Hicks and may <br> partly account for some of the errors into which he has fallen <br> Further comparison however would have shown him that the strata <br> are here isoclinally folded ; that is they have been thrown into an <br> anticline which has been bent over to the south-east so that the <br> strata in the south-eastern half of the fold are inverted figs 1 2 <br> p 268 That this is the case was proved by Mr Peach and myself <br> in the identification of the same beds on the two sides of the arch In <br> particular the peculiar group of shales or schists immediately below <br> the conglomerate on Ramsey Sound reappears at Porth-lisky The <br> conglomerate accompanies them ; but at the latter locality it has been <br> cut out by the granite It appears however a short way inland in <br> the Allan valley and on the east side of the granite at Ogof-llesugn <br> The reversed dip continues along the coast-line ; but the beds are <br> eventually seen to right themselves and they appear in normal <br> order to the east of Caer-fai I shall return to this interesting <br> structure in the second part of this paper p 309 f <br> Dr Hicks figures this junction as an unconformability of the Cambrian <br> conglomerates on the Pebidian Beds But he reverses the visible dip making <br> tbe rocks inclined towards the sea instead of towards the land Quart Journ <br> Geol Soc vol xxxiii p 236 This subject is again referred to in the text <br> t It may be proper to notice here that the structure above described proves <br> that Dr Hicks's estimate of the visible thickness of his Pebidian group is <br> greatly exaggerated He makes the thickness at least 8000 feet Quart Journ <br> Geol Soc vol xxxiv p 159 Were the beds absolutely vertical all the way <br> they could not be more than 4000 feet ; for they extend across a belt which to 36928886 113681 51125 Page 287 Text 39 http //www biodiversitylibrary org/page/36928886 1883 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 39 1883 Geology Periodicals Smithsonian Libraries bhl page 36928886 dc identifier http //biodiversitylibrary org/page/36928886 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-16 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13204715765 2015-08-26 13 55 24 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1883 Photos uploaded from Flickr by Fæ using a script | ||||
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