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| Keywords: The Quarterly journal of the Geological Society of London (13935545441).jpg 452 <br> PROCEEDINGS OP THE GEOLOGICAL SOCIETY Apr 11 <br> Pq <br> GQ <br> Ph <br> §i <br> dotic portions of the latter and in two classes <br> of true lodes ” one of which crosses the strata at <br> right angles to their strike forming the so-called <br> fissure-veins of the Keweenau Point and Eagle <br> Eiver districts ; while the other includes such <br> veins as run with the formation and are found <br> in the Ontonagon district These are very irre- <br> gular in character ; and the fact of their being <br> veins can only be made out by their relations to <br> the containing rocks as developed in deep work- <br> ing the surface appearance being that of irre- <br> gular masses of epidote -breccia continually <br> varying in thickness although capable of being <br> traced for considerable distances In the fissure- <br> veins the metal occurs in comparatively smooth <br> platy masses of all sizes and comparatively free <br> from intermixed rock ; while in the Ontonagon <br> lodes the masses are rough and on a very large <br> scale arborescent in form and usually contain <br> large adherent and included fragments of the <br> vein-stone ” a breccia of epidotic rock and <br> quartz ; but in either case they may attain a <br> great size and at times a weight of several <br> hundred tons In the cupriferous amjgdaloids <br> of Portage Lake masses of great size are not <br> found the largest being that discovered about <br> two years since in the Mesnard location which <br> weighed about 18 tons and lay loose on the <br> drift covering the rock In addition to the <br> masses thin sheets of metal are common wherever <br> narrow transverse cracks occur in the rock <br> either forming masses of tangled crystals with <br> a serrated edge or when of large size being <br> more compact and not unlike worn-out copper <br> sheathing The metallic kernels of the amyg- <br> daloids are rarely solid but form thin shells <br> moulded to the wall of the cavity or to the <br> crystals of some mineral previously deposited <br> usually carbonate of lime In the conglome- <br> rates in like manner the metal usually incrusts <br> the pebbles sometimes completely investing <br> but never entirely replacing them When cry- <br> stallized in its oAvn form the copper has also a <br> great tendency to appear in hollow crystals the <br> simplest solid forms being formed in the hol- <br> lows of the larger masses A fine example of <br> this has been recently furnished by the great <br> mass of the central mine which on one of the <br> cuts disclosed a druse full of nearly perfect <br> crystals of tetrahedral form without any se- 36164899 111477 51125 Page 452 Text v 22 http //www biodiversitylibrary org/page/36164899 1866 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 22 1866 Geology Periodicals Smithsonian Libraries bhl page 36164899 dc identifier http //biodiversitylibrary org/page/36164899 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 N02/13935545441 2015-08-26 06 52 57 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1866 Photos uploaded from Flickr by Fæ using a script | ||||
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