PBE-CAMBKIAN EOCKS OF ST. DAVIDS. 329 



the arguments formerly relied upon by Dr. Hicks to prove its meta- 

 morphic origin were certainly untenable ; but that was admitted by 

 Dr. Hicks himself, so that the Director-General had merely stated 

 what was well known to most petrologists. At the same time there 

 was a something, hard to describe in words, that differentiated this 

 crystalline rock of St. David's from all the undoubted granites with 

 which the speaker was acquainted, and he still thought it probable 

 that it, like the granitoid rock of Twt Hill, Llanfaelog (Anglesey), 

 Edcal Hill, &c, was really metamorphic. Next, as regards its age : 

 he had carefully examined two out of the three sections relied on by 

 the Director-General to prove the intrusive nature of the rock. Of 

 intrusion he had been unable to see the slightest evidence, whether 

 at Porth-clais or Ogof-Llesugn. The appearances at the latter place 

 were undoubtedly difficult to explain ; but an intrusion of the Dime- 

 tian appeared to him a most improbable suggestion. Further, the 

 present materials of the Cambrian conglomerates of Dr. Hicks had 

 evidently been derived from the destruction of quartzo-felspathic 

 rock, and the quartz-grains corresponded remarkably as to their 

 cavities &c. with the quartz-grains in the Dimetian. The micro- 

 scopic structure of this conglomerate bore a singular resemblance to 

 that of some conglomerates in North Wales which had been proved 

 to be formed out of the ruins of a more ancient granitoid rock. 

 Hence it was almost certain the Dimetian was older than the con- 

 glomerate. Lastly, as regards the separation of the Pebidian from 

 the Cambrian, to himself there appeared to be an unconformity 

 at the base of the quartz conglomerate; certainly there was an 

 entire change in the lithological character of the deposits. In the 

 Pebidian volcanic material predominated, the finer detrital beds 

 were more indurated, and there was an incipient metamorphism. 

 The conglomerate introduced a series of beds different in aspect, 

 colour, materials, and condition. He did not say, and never had 

 thought, that the break between Cambrian and Pebidian was neces- 

 sarily a very great one ; but it was perhaps as good physically as 

 that between Upper and Lower Silurian, and, at any rate, a better 

 physical break than could be found anywhere between itself and the 

 Llandovery. Hence he must consider the two cardinal points of the 

 Director-General's paper to be " not proven." Some mistakes, most 

 of them already admitted, he had detected in Dr. Hicks's work ; but 

 considering the date and the circumstances it was a very small dis- 

 credit to have erred occasionally. 



Prof. Lapwoeth thought that in the stratigraphical part of the 

 subject the author had failed to prove his point with regard to the 

 intrusion of the granitic rock. The supposed intrusions appeared to 

 be nothing but overturn faults, such as occur in all old crumpled 

 districts. He asked if the name Cambrian was to be carried down 

 indefinitely. He had found rocks resembling these Pebidian volcanic 

 beds underlying fossiliferous Cambrian strata in Central England 

 and round the Longmynd. 



The Author said that he was placed at a disadvantage by his 

 paper being split up into two portions ; the second part would reply 



