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| Keywords: The Quarterly journal of the Geological Society of London (14075838925).jpg 462 <br> J H COLLIifS OjST the SEEPENTIIfE AoST <br> Porthalla <br> Fault <br> Serpentine <br> in <br> <br> <br> J <br> SQ <br> CO <br> The general strike of the Lizard rocks referred to <br> is a few degrees to the north of west the prevail- <br> ing dips being to the east of north At Porthalla <br> on the contrary the general strike is to the east <br> of north i e as nearly as possible at right angles <br> to the direction of the Lizard rocks <br> The band of granulite in the micaceous group <br> which appears to Prof Bonuey to be a conform- <br> able bed of that series formed under similar con- <br> ditions to the granulitic group of the Lizard <br> seems to me to be distinctly unconformable and <br> to have the character of an intrusive vein pene- <br> trating the talcose schists as indicated in <br> sections figs 2 and 3 I beheve in short that the <br> Lizard rocks may be Archaean but that those of <br> Porthalla are of much later origin and most pro- <br> bably Lower Silurian <br> The rocks beyond Hickes's quarry offer no <br> special feature of interest As already stated <br> they consist mainly of hornblende schist of the <br> banded type interspersed with occasional bands <br> of serpentine the largest exposures of which <br> latter are in the broken ground which succeeds <br> the fault at Porthalla and in the little cove to the <br> south of Polkerris In the section fig 3 I give an <br> ideal rej resentation of the country from Porth- <br> alla to Pencra Head on a line which passes a <br> little to the south of this cove This section is <br> given as the result of a careful examination of the <br> country on several different occasions It is of <br> course partly hypothetical ; but I believe it is in <br> the main correct <br> Veins of Gahhro <br> These I have not yet seen in a perfectly satis- <br> factory manner ; but there are several bands or <br> what I believe to be gabbro traversing the schist <br> between the quarry and Dranna Point I have <br> examined the cliffs on several occasions with the <br> view of ascertaining the true nature of these <br> veins; but the swell has always prevented me <br> from taking the boat close up to the rocks I <br> have however repeatedly found on the shore <br> close to the quarry loose masses of the schist tra- <br> versed by veins of undoubted gabbro In appear- <br> ance the gabbro does not seem to differ at all <br> from the IS'ewer gabbro of Coverack described <br> by Prof Bonney 36941281 113697 51125 Page 462 Text 40 http //www biodiversitylibrary org/page/36941281 1884 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 40 1884 Geology Periodicals Smithsonian Libraries bhl page 36941281 dc identifier http //biodiversitylibrary org/page/36941281 smithsonian libraries Information field Flickr posted date ISOdate 2014-04-30 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/14075838925 2015-08-26 05 57 14 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1884 Photos uploaded from Flickr by Fæ using a script | ||||
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