J. H. Collins — Cornish Seiyentines. 299 



Geological Society of London) ^ aside by a repetition of the dogmatic 

 assertion that the serpentine here " has forced itself through and 

 among the schists," and " actually infuses itself into their com- 

 position at and near their junctions, so as to form a kind of transition 

 between the two rocks of opposite origin, which Mr. Collins has 

 very evidently mistaken for serpentine in a less altered form, thus 

 seeming to favour his mistaken conclusion of the serpentine being 

 only an altered slate." 



I may here remark that the expression " the serpentine being 

 only an altered slate " does not quite accurately convey my meaning, 

 although, of course, I find no fault with Mr. Somervail for using it. 

 What I believe is, not that " the slate " has been altered into ser- 

 pentine, but that, of an originally differing series of conformable 

 bedded rocks, some beds have been converted into that peculiar 

 variety of hornblende schist which characterizes the locality, others 

 have been converted into true serpentine, and others again into 

 a rock of intermediate character. In fact I consider that we have 

 here the final results of a long series of processes of "selective 

 metamorphism," the same agents acting for the same times on dis- 

 similar masses, and so giving rise to dissimilar products. Moreover, 

 as there were originally transition beds of the original strata, so now 

 there are transition results in all stages, so affording complete series 

 of passage specimens, not "apparent" merely, but veritable and 

 real. In all these cases it seems to me likely that a hornblendic 

 mineral has been first formed, and that the conversion of this into 

 serpentine is the final change. 



It is, moreover, obvious that such reactions might take place, 

 under suitable circumstances, so as to change a rock mass into 

 serpentine quite irrespective of its mode of origin, whether igneous 

 or aqueous, and one has not to go outside the borders of Cornwall, 

 perhaps not outside the borders of the Lizard district, to find ex- 

 amples of both classes of rocks which have undergone this change. 



Speaking of the serpentine more especially of Coverack, Professor 

 Bonney says, in his recent communication (Geol. Mag. 1884, p. 409) : 

 "If there be in Nature any indications from which we can assert the 

 intrusive character of any igneous roclc lohatever, we have these indica- 

 tions in the case of the Lizard serpentine and the associated sedimentary 

 series." 



1 by no means deny that this description is fairly enough ap- 

 plicable to the Coverack serpentine, and I do not dispute that this 

 particular serpentine has resulted from the alteration of an igneous 

 intrusive rock, as stated by the Professor. Still, I agree with Dr. 

 Sterry Hunt in thinking that such appearances (of intrusion) may 

 very often, if not usually, be "explained by subsequent movements of 

 the strata in which the serpentines are included " {op. cit. conclusion). 



Moreover, I assert that the serpentinous beds of Porthalla, Mullion, 

 and the greater part of the Lizard district do not possess the un- 

 mistakeable indications alluded to, but, on the contrary, they have 

 the closest possible inter-relations with the hornblende-schists of the 

 same localities, both stratigraphically and chemically. 



1 Quart. Journ. Geol. Soc. 1884, vol. xl. pp. 458-471. 



