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| Keywords: The Quarterly journal of the Geological Society of London (13960511653).jpg HORNBLENDE-SCHISTS ETC OF THE LIZARD 519 <br> 33 Notes on the Hornblende-schists and Banded Crystalline <br> Rocks of the Lizard By Major-General C A M c Mahon <br> F G S Read May 22 1889 <br> I haye visited the Lizard on three occasions namely in 1887 in <br> company with several Members of the Geologists' Association under <br> the able guidance of Messrs Howard Fox F G S and E A Wiinsch <br> F G S ; in 1888 by myself; and in February of the present year <br> in company with Mr Howard Fox to whom I feel under the <br> greatest obligation his intimate acquaintance with the Lizard <br> rocks and his local knowledge rendering his aid in the field ex- <br> tremely valuable <br> On each occasion I collected numerous specimens of the rocks and <br> studied thin slices of them under the microscope during the intervals <br> between my visits so that I have had an opportunity of correcting <br> the impressions made in the field by microscopic work in the study <br> and of again testing ideas formed in the study by fresh observations <br> in the field I have examined under the microscope over ninety <br> thin slices of my own specimens nearly fifty have been lent me by <br> Mr Howard Pox and Mr J J Harris Teali kindly placed those of <br> his own collection at my disposal <br> Before stating the results of my own investigations I think it desir- <br> able to refer briefly to the views expressed by previous observers <br> Sir Henry De la Beche's opinion may be gathered from the following <br> extract from his ' Report on the Geology of Cornwall and Devon ' ” <br> If it were not for the occurrence of the hornblende slate in the <br> conglomerate of the Nare Point we might suppose that it the horn- <br> blende slate was a mass of that trappean or ancient volcanic ash <br> which is detected so abundantly amid the grauwacke of Devon and <br> Cornwall upon which the mass of serpentine and diallage rock now <br> nearly covering it up has been poured in a melted state ; and that <br> being thus retained long beneath it in a heated condition the water <br> amid its loose laminse prevented from escape upwards by the hot <br> rock above the hornblendic and felspathic particles ol which it was <br> composed arranged themselves into crystalline forms the mass retain- <br> ing its original laminated structure It must however be <br> confessed that unless we suppose the hornblende slate in the <br> conglomerate of the Nare Point to be derived from some other source <br> this explanation is not so good as could be desired <br> The blocks in the conglomerate alluded to are said by De la Beche <br> in another place Report p 94 to be generally decomposed and <br> his correlation needs confirmation especially by the modern methods <br> of microscopic investigation ; but even if the rocks which supplied <br> the boulders were satisfactorily shown to be the hornblende- <br> Report p 34 36940348 113696 51125 Page 517 Text 45 http //www biodiversitylibrary org/page/36940348 1889 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 45 1889 Geology Periodicals Smithsonian Libraries bhl page 36940348 dc identifier http //biodiversitylibrary org/page/36940348 smithsonian libraries Information field Flickr posted date ISOdate 2014-04-21 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/13960511653 2015-08-26 05 52 12 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1889 Photos uploaded from Flickr by Fæ using a script | ||||
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