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THE BASAL WRECKS AND REMNANTS OF EXTINCT VOLCANOES, 



ALONG THE SOUTH- WEST COAST OF CORNWALL. 



By THOMAS CLARK. 



Brief Historical Sitmmart. 



The study of igneous action in Cornwall has centralized 

 itself at its most fascinating development, at the Lizard, but the 

 manner of its origin and ultimate results will, I think, be better 

 answered by those who study its minor developments further 

 afield before attacking it at its culmination, which, in my opinion, 

 should be dealt with last and not first. 



Fifty years ago Sir Henry De la Beche marked as green- 

 stone some of the headlands on the South-west coast of Cornwall. 

 These generalizations remained unchallenged till about ten 

 years ago, when Professor Bonney, having procured and ex- 

 amined specimens of the Lizard rocks, pronounced them Archsen, 

 with more recent intrusions of volcanic matter, such as Serpen- 

 tine, &c.* 



After the publication of Professor Bonney's paper, I spent 

 several days with Mr. J. H. Collins in examining the rocks about 

 the Lizard and Porthalla, a locality I have had occasion to visit 

 many times since. The outcome of our visit was a paper by 

 Mr. Collins,! in which he endeavoured to show that the rock 

 formation of the Lizard district was principally due to metamor- 

 phosed sedimentary rocks. Now, though the visit was made 

 conjointly, the paper was not conjointly written, for I differed 

 so far from the conclusions of Mr. Collins that I at once prepared 

 a paper for this Institution, in which I gave my opinions for 

 believing they were of volcanic origin, and not altered sedi- 

 mentary rocks, and this view I endeavoured to sustain by rock 

 specimens and microscopical sections of the rocks themselves. 

 And this paper was read at the Monthly Meeting on April 1 8th, 

 1887. 



* Quat. Jour. Geo., 1877 and 1884. 

 f Quat. Jour. Geo. Soc, Aug., 1884. 



