Vol. 52.] THE ROCKS OF THE LIZARD DISTRICT, 17 



3. The Serpentine, Gneissoid, and Hornblende Bocks of the Lizard 



District. By T. G. Bonnet, D.Sc, LL.D., F.B.S., F.G.S., 



Professor of Geology in University College, London, and Fellow 



of St. John's College, Cambridge. (Bead November 6th, 



1895.) 



[Plate I.] 



Contents. p age 



I. Introductory . 17 



II. The Genesis of the Hornblende-schists 18 



(a) Inclusions in the Hornblende-schist at Porthoustock Cove 19 



(b) Inclusions in the Hornblende-schist south of Kilcobben Cove ... 20 



(c) Quarry on the descent to Mullion Cove 20 



III. The Genesis of the ' Granulitic Group ' 22 



IV. Eelations of the Serpentine to (a) the ' Granulitic Group,' (b) the 



Hornblende-schists « 24 



V. Conclusions 40 



TI. Appendix 42 



(a) Miscellaneous Notes 42 



(b) Age of the Lizard Rocks 47 



I. Introductory. 



In 1891 a communication on the rocks of the Lizard from General 

 M c Mahon and myself was honoured with a place in the Society's 

 Journal. 1 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 hornblendic group ' as stratified basic tuffs, subsequently 

 metamorphosed, was ' the better working hypothesis/ 2 But, even in 

 that interval, as will be seen by a note appended to the paper, 3 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 in- 

 superable 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, 4 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 con- 

 fusion. 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 

 in other localities. I felt, indeed, so much confidence in the general 



1 Quart. Journ. Geol. Soc. vol. xlvii. (1891) p. 464. 



2 Op. cit. p. 480. 3 Op. cit. p. 479. 

 4 Quart. Journ. Geol. Soc. vol. xlix. (1893) p. 199. 



Q. J. G. S. No. 205. c 



