PEBIDIAN ROCKS OP PEMBROKESHIRE. 155 



8. Purplish and greenish chloritic-looking bands with a schistose 

 or rude cleavage structure, all apparently, on microscopical examina- 

 tion, highly altered basaltic rocks. 



9. The crystalline limestone bands described in our former paper. 

 Nos. 5, 6, 7, and 8 are best seen in the coast section along the 



east side of Porthlisky Harbour, where they may be examined 

 alternating with one another, but not exactly in the above order. 



Intruded amongst all these various series are to be found occasion- 

 ally dykes of greenstone, porphyry, and dolerite. 



The indurated ashy shales showing frequently distinct lines of 

 lamination and the so-called chloritic schists, mentioned in the 

 above series, ever since 1864, when Mr. Salter and I first noticed 

 their persistent strike in one direction over a large area, have con- 

 tinually caused doubts to be raised in our minds as to their true 

 nature and origin. 



In 1865 I forwarded notes to Mr. Salter, in which I mentioned 

 facts to show that some at least of these were intrusive ; and this 

 caused him to communicate a note to the ' Geological Magazine ' 

 for September 1865, in which he states that I had proved that we 

 were previously in error in supposing them to be truly interbeddecl, 

 by finding portions of the schists entangled in the so-called Syenite. 

 Subsequently examinations, however, seemed to show that there 



the ridge and at a very high angle; hence a great thickness is traversed in 

 crossing the section from St. David's to the extreme point in St. Bride's Bay, 

 beyond Porthlisky. At Porthlisky Harbour the beds are probably repeated by 

 folds ; otherwise the changing characters noticed in the sediments indicate that 

 we have on the whole a continuously ascending series. It is satisfactory to note 

 also that the further critical examinations which have been made of the rock- 

 specimens go to confirm the opinions I previously expressed concerning the 

 sedimentary origin of the majority of the rocks in this formation ; whilst, on 

 the other hand, some doubts have been cleared up, especially as to the true 

 nature of the interstratified dark bands, which are of considerable importance. 

 I have great pleasure in adding the following Notes by Prof. Bonney, M.A., 

 F.G.S. (made on a separate set of slides), as it will be seen that they are entirely 

 confirmatory of the observations previously made by Mr. T. Davies, F.Gr.S., and 

 myself: — 



Granitoid Sock, Dimetian (No. 4). "I have no doubt this is an altered rock 

 not of igneous origin. It seems, however, much altered, like many specimens of 

 gneiss. It contains much quartz, a fair amount of felspar, in which I recognize 

 both orthoclase and plagioclase, and a little viriclite, probably replacing a black 

 mica. Here and there I note an approach to a graphic structure." 



Quartziferous Breccias, Dimetian (No. 5). " A rock of distinctly clastic origin, 

 containing fragments of quartz and felspar, variable in size, generally angular 

 and subangular. There is also a little of a green mineral probably allied to 

 chlorite. I recognize some plagioclase among the felspar. I see nothing to 

 suggest a pyroclastic origin ; but it appears to be the kind of rock which might 

 come from the denudation of a gneiss or granite where the materials had not 

 been transported very far, a sort of ' arkose.' It looks to me as if it had been 

 rather crushed since solidification." 



Quartz Schists, Dimetian (No. 6). " These are difficult and interesting rocks. 

 They consist mainly of quartz and felspar with a little viriclite, the former, per- 

 haps, rather predominating. ]n parts they exhibit a sort of graphic structure ; 

 still I regard them as altered rocks and belonging to the same group as No. 4. 

 There is rather too much felspar for a normal quartzite." 



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