Keywords: The Quarterly journal of the Geological Society of London (12980957865).jpg 1858 ABICH ETNA 127 <br> mass becomes more coherent and passes into a black pitchstone- <br> like crust which covers the sides of the dyke with a regular layer of <br> a more or less glassy substance some inches thick and as black as <br> coal On the outside of the dyke the black glassy crust showed on <br> its uneven surface and imbedded in it as in a paste a great quantity <br> of small and great fragments of the rocks composing the horizontal <br> beds through which the dyke had passed The magnetic power <br> of this dyke was considerable Advancing still more along the crest <br> of Monte Zoccolaro and bending a little on a more gentle slope of a <br> detached part of that enormous ridge towards the valley I was <br> struck by the curious phaenomenon of which fig 11 gives a very <br> Fig 11 ” Grotta del Subi Legno on the side of Monte Zoccolaro <br> true representation A dyke of a mean diameter of 6 feet consisting <br> of a compact felspathic lava and trending N 35° W suddenly stops <br> the path The surface of the outside is scorified exhibiting a <br> smoothly rounded kidney-shaped crust When turning round that <br> curious massive wall which terminates at the crest in a kind of <br> pad overhanging a little towards the south-eastern side I perceived <br> that there was an immediate passage from the mass of the perpen- <br> dicular dyke into a regular layer or bed of the same stone towards <br> the eastern side This layer from its beginning at the top of the <br> dyke went down with a mean inclination of 25° and regained an <br> almost horizontal position from 6° to 0 The masses which once <br> fitted the corner between the dyke and its detached layer are partly <br> removed having given way to a great extent by lateral subsidence <br> The cavern thus formed is somewhat spacious and has the name of <br> ' Grotta del Subi Legno; the physical nature of the roof of this <br> cavern is that of a half-smolten scorified lava ; great stalactites in <br> huge masses hanging down from the roof correspond to former <br> depressions in those fragmentary layers over which the lava pouring <br> out of its perpendicular channel had first to flow That lava- <br> stream shows how lava- currents ” suppose they are given out by <br> rents of considerable length ” are capable of forming regular layers of <br> even 25° inclination without the slightest difference in the internal <br> structure of the rock both of the dyke and of the layer On its <br> outer surface this lava-bed shows the same scorified appearance as <br> on the surface visible in the interior of the cavern <br> The nature of the mass which forms the dyke shows some in- <br> teresting peculiarities The rock is compact and highly crystalline <br> In the axial region a spongy zone of pores of considerable size runs <br> upwards; these pores are hollow and of the same appearance as 36161666 111474 51125 Page 127 Text v 15 http //www biodiversitylibrary org/page/36161666 1859 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 15 1859 Geology Periodicals Smithsonian Libraries bhl page 36161666 dc identifier http //biodiversitylibrary org/page/36161666 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-07 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12980957865 2015-08-26 14 51 08 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1859 Photos uploaded from Flickr by Fæ using a script |