The Serpentine, Gneissoid, and Hornblende Rocks of the Lizard District

Abstract

I. Introductory In 1891 a communication on the rocks of the Lizard fron General McMahon and myself was honoured with a place in the Society's Journal. As therein stated, we were of opinion, at the time of our visit to Cornwall (August, 1890), that to regard the banded members of the ‘the hornblendic group’ as stratified basic tuffs, subsequently metamorpohosed, was ‘ the better working hypothesos.’ But, even in that interval, as will be seen by a note appended to the paper, some doubts as to the correctness of this conclusion had already arisen in my mind, for a visit to Sark in the spring of 1891 had suggested explanations of certain difficulties which hitherto had seemed insuperable in an alternative hypothesis. Accordingly I became anxious to see how the old puzzles looked in the new light, and besides this a very important paper by my friends Messrs. Howard Fox and J.J. H. Teall, subsequently published in this Journal, made it a necessity for me to study the sections of which they had given so lucid a description. for, if their interpretation of these were correct, the geology of the crystalline rocks of the Lizard peninsula would be thrown (as it seemed to me) into hopeless confusion. The authors, indeed, restricted their conclusions to the sections which they had described; but it appeared to me, for reasons which will be given hereafter, that no such limitation was possible, and that if they were right I must have misinterpreted the evidence