Vol. 60.] THE LLYN-PADARH DVKES. 375 



place, were certainly injected before these great earth-movements 

 had died away. 



To sum up the field-evidence on this point, we find in these 

 dykes unmistakable signs of dynamic metamorphism and de- 

 formation. It would not be expected that those portions of the 

 dykes which were firmly held in the Llyn-Padarn ridge would be 

 so profoundly affected by the post-Bala movements as those enclosed 

 in the more yielding sedimentary strata towards the south, and this 

 agrees precisely with what appears to have taken place. The pro- 

 gressive examination of these dykes from one extremity to the other 

 furnishes many interesting examples of the effects of varving degrees 

 of pressure-metamorphism, to certain of which attention will shortlv 

 be drawn. 



It must not be supposed, however, that highly-sheared and altered 

 ' greenstones' do not. occur in the Llyn-Padarn ridge. I have found 

 several instances of these, and it is suggested that they may belong 

 to a still older group. 



I do not propose to reopen the controversy with regard to the 

 stratigraphical succession in this district, but taking the conglo- 

 merates on either side of the Llyn-Padarn ridge as the base of the 

 Cambrian, the evidence for the existence of pre-Cambrian greenstones 

 will now be considered. Previous observers have called attention 

 to the occurrence of fragments of basic igneous rocks in the con- 

 glomerates, 1 and have expressed some difficulty in refering these to 

 their origin. The Eev. J. F. Blake has described the occurrence at 

 Bryn Efail, on the north side of the Llyn-Padarn ridge, of felsite 

 intrusive in a rock which he believed then to be a slate," but 

 Miss Raisin has since shown this to be a sheared ' greenstone ". ' It 

 should perhaps be mentioned that the latter observer failed to see 

 any vidence of the intrusion of the felsite into the i greenstone \ 

 Without, however, entering into the discussion of the Bryn-Efail 

 section, about which a great deal has been written by the above- 

 mentioned authors, the following fact appears to the present writer 

 to furnish independent proof that there is in the Llyn-Padarn rid^c 

 a ' greenstone ' older than the quartz-felsite. 



Passing along the road which runs from the bridge at the lower 

 end of Iiyn Padarn along the eastern shore of the lake, near the 

 point where this road crosses the slate-railway (marked A on the 

 sketch-map, p. 376), there is an exposure of ' greenstone ' which 

 appears to have been opened up by blasting comparatively recentlv. 

 To all appearance, this rock resembles the ordinary basic dvkes which 

 penetrate the quartz-felsite in this locality, but it has evidentlv 

 been much sheared. 



1 T. G. Bonney & C. A. Raisin, ' On the Belatious of some of the Older 

 Pragmental Rocks in North-Western Caernarvonshire' Quart. Journ Geo! 

 Soc. vol. 1 (1894) p. 578. 



2 ' On the Cambrian & Associated Rocks in North-Western Caernarvonshire ' 

 Ibid. vol. xliv (1888) pp. 283, 284. 



3 ' On the Lower Limit of the Cambrian Series in Xorth-Western Caer- 

 narvonshire ' Ibid. vol. xlvii (1891) p. 337. 



