On the Schistose Volcanic Rocks occurring on the west of Dartmoor, with some Notes on the Structure of the Brent Tor Volcano

Publisher Website
Google Scholar
Abstract
After examination of the schistose beds of rock on the western margin of the Dartmoor granite, I experienced great difficulty in coming to any satisfactory conclusion concerning the origin and real nature of many of them. These rocks had already been described by Sir Henry De la Beche, in his Report on the Geology of Cornwall, Devon, and W. Somerset, as schistose ashes; and his well-known keenness in detecting lithological peculiarities naturally induced me to accept his opinion, especially as it seemed in some instances to be a very correct one. There was, however, one point which caused me considerable perplexity. I could not reconcile the very frequent occurrence of a densely amygdaloidal structure with the persistently schistose character of these rocks. If the amygdaloidal condition implied a once vesicular structure, and if the rocks should on this account be regarded as lavas, how then was the schistose character to be accounted for? I was not then acquainted with any instance of schistose lava. On the other hand I could not understand why, if these rocks were ashes, they should be amygdaloidal. In my memoir* on the eruptive rocks of Brent Tor and its neighbourhood I endeavoured to account for the schistose structure in lavas, and for the amygdaloidal condition in ashes, and in many places expressed my doubt about the true character of these rocks. Ever since those lines were written I have been anxious to ventilate this matter, and, if possible, to arrive at a more satisfactory solution

This publication has 0 references indexed in Scilit: