PRE-CAMBRIAN ROCKS OF ST. DAVID'S. 331 



morphosed before the deposition of the latter. He pointed out the 

 existence of great masses of agglomerate in the midst of the supposed 

 intrusive masses. 



Mr. Peach stated that, taking Dr. Hicks's own sections, published 

 in the Quart. Journ. Geol. Soc. vol. xxxiv., it was clear that the strata 

 are repeated by a great inverted fold, and the beds can be identified 

 member by member (from Dr. Hicks's description) on the two 

 sides of the axis. From these sections of Dr. Hicks's he argued 

 that the Cambrian conglomerate rests always on the same member 

 of the underlying beds, and there could be no unconformity. He 

 regarded the so-called Pebidian pebbles as segregations and not 

 pebbles. 



Mr. Httoleston stated the results of an examination made of the 

 district in 1877 in company with Dr Hicks and the late Mr. Taw- 

 ney. At that time Dr. Hicks had not recognized the volcanic origin 

 of the Pebidians. No one could suppose the Pebidians to be of suffi- 

 cient importance to constitute a system by themselves ; and the great 

 question was whether they should be grouped with the Cambrian or 

 the Archaean. He had difficulty in recognizing the supposed uncon- 

 formity between the Cambrian and the Pebidian, and he thought 

 that the volcanic series was the natural base of the Cambrian system. 



Mr. Teall called attention to the fact that diabase dykes in the 

 granite were represented on Prof. Geikie's map as terminating at 

 the junction with the Cambrian. He asked if this did not imply 

 that they were Pre-Cambrian and of the age of the diabase tuffs. 



Mr. Topley in reply stated that the faults invoked by Dr. Hicks 

 would account for the non-passage of a dyke from the granite 

 into the Cambrians. Dr. Hicks had not distinguished between 

 local and regional metamorphism. The specimens from the conglo- 

 merate exhibited by Dr. Hicks were certainly exceptional ; but the 

 great mass of the conglomerates are of quartzose character. Local 

 and small unconformities between the Cambrian conglomerates and 

 the main volcanic group (Pebidian) had been admitted both at this 

 and at the last meeting ; but he differed from Dr. Hicks as to the 

 great significance to be attached to them. 



Dr. Callaway objected to Prof. Geikie's views as to bleaching 

 and induration being proofs of local metamorphism ; he regarded 

 them on the contrary as evidence of faulted junction, the result of 

 pressure and the infiltration of water. He did not think Dr. Hicks 

 was justified in insisting on the Arvonian formation. He remarked 

 that the key found by Dr. Hicks at St. David's had supplied us with 

 an explanation of most of the similar Archaean series in England 

 and Wales, which was a great confirmation of the truth of the theory. 



Mr. Rtttley said that some of the felsites of the district resembled 

 certain spherulitic rhyolites. He thought that they represented 

 a transition between granitic rocks and ordinary rhyolitic lavas. 

 Most of the Welsh lavas of the same kind with which he was 

 acquainted were of Lower Silurian age. 



Mr. T. Davies could not agree with the author in regarding the 

 so-called Dimetian as a granite. It contained no mica, nor had it 



