VOLCAJ^IC SERIES OE ST. DAVIDS. 



269 



various parts of the Archaean from which they were derived, though 

 that might not be the immediately underlying part, as he had long- 

 ago pointed out in the case of the jS^orth-Wales sections. 



Appealing to particular sections he explained the proofs, from the 

 fluting and crushing of the rocks, &c., that the junction seen at 

 Perth Clais was a fault ; but at Ogof Golchfa evidence of the original 

 unconformable junction could still be made out, though the Cambrian 

 was much crushed and shifted by the coming together of beds of 

 unequal texture, and the purple ash-like schist on which it rested 

 was squeezed out during earth-movements by being in contact with 

 the unyielding conglomerate. There seemed to be here, as at Nun's 

 "Well, signs of long and deep oxidation of the rock on which the 

 Basement Eeds of the Cambrian rested. At Ogof Llesugn he thought 

 that an unconformable junction could be seen, though it was tra- 

 versed by numerous step-faults, so that much depended upon the 

 position of the observer when drawing the section ; while the sup- 

 posed passage or intercalations in the cliff-section close by he con- 

 sidered to be only a passage between the gneissic and porcellaneous 

 felspathic rock, with local changes due to crush and consequent later 

 alteration, the Cambrian conglomerate being quite distinct, and the 

 supposed alternation of Cambrian and Archaean only an included 

 fragment or " horse " of conglomerate caught in a fault and cut 

 back by denudation. 



Mr. H. W. Williams failed to recognize some of the Author's 

 sections, although well acquainted with the locality. 



The Author said that the main point between himself and 

 Dr. Hicks was as to the relations of the conglomerate to the under- 

 lying Pebidian. He hoped to go over the ground some day with 

 him and Mr. Williams. He had not worked the section in patches, 

 but had traced it continuously throughout the whole district. He 

 had listened with admiration to all that Dr. Hicks had said about 

 the enormous faulting of the fossiliferous Cambrian, but failed to 

 see how it bore on the subject. To please Prof. Hughes he was 

 ready to admit any number of faults, and he also agreed with 

 Dr. Hicks as to shearage. He was glad to find that Prof. Blake 

 practically agreed with him as to the relations of Pebidian to 

 Cambrian. He was well acquainted with the existence of step- 

 faults, and thought that Prof. Hughes had misunderstood his 

 meaning ; the overlap of | mile was due to step-faulting. He 

 maintained that his reading of the Ogof Golchfa section was correct, 

 and spoke of the bevelling-off of the edges of the beds. 



The evidence of Carn-ar-Avig neither Dr. Hicks nor Prof. Hughes 

 had touched. It was perfectly clear that " tuffy '' ash and lavas 

 might be seen overlying the conglomerate. He submitted a map, 

 which was on the table ; but in a volcanic region it was not cas)"- 

 to map systematically, since this was not a regular series of beds as 

 maintained bj^ some. 



