254 PKOF. C. LLOYD MOEGAN Olf THE PEBIDIAN" 



on the volcanic condition of the Pebidian, the uppermost Pebidian 

 beds ah-eady foreshadowing the sedimentary conditions of the 

 Caerfai beds. 



And here I think it well to draw attention to the amount of 

 break for which Dr. Hicks contends. According to Dr. Hicks the 

 Pebidians were (1) deposited as a volcanic series, (2) upheaved into 

 dry land, and also (3) metamorphosed to very much their present 

 condition before (4) they were denuded to form coast-lines of an 

 Archaean land, which (5) once more sank beneath the sea and (6) 

 were overlain un conformably by the beach-deposit of the Cambrian 

 conglomerate. Such is Dr. Hicks's contention. But it is right to 

 add that at times he writes as if he held a very different view. 

 For example, in his answer to Dr. Geikie (Q. J. G. S. xl. p. 536), he 

 says : — " Whether the volcanic fires had completely expended them- 

 selves or not before the conglomerates were deposited may be an 

 interesting point ; but it is virtually of no importance in regard to 

 the questions at issue." On reading this I thought I must have 

 misunderstood Dr. Hicks's previous statements. But no ! They 

 are quite clear. So also is the testimony of his map. And I 

 therefore am in some doubt as to which statement represents Dr. 

 Hicks's present view. Taking, however, the former, so distinctly 

 formulated and reiterated, I must distinctly state that I could find 

 no evidence to justify it. Coming to St. Davids fresh from a 

 study of the beach-conditions of the Basement Beds of the Trias in 

 the Bristol district, I was impressed with the very different nature 

 of the break between Pebidian and Cambrian in Pembrokeshire. 



The relation of Pebidian to Cambrian is therefore, in my opinion, 

 that of a volcanic series, for the most part submarine, to the suc- 

 ceeding sedimentary strata which are introduced by a conglomerate 

 formed in the main of foreign pebbles borne onward by a current 

 which swept the surface of, and eroded hollows and channels in, 

 the volcanic tuffs and other deposits. 



The last question which arises on this head is whether we should, 

 as Dr. Geikie proposes, abandon altogether the term Pebidian ; and, 

 further, if we retain it, what value we should assign to it. I think 

 that to abandon it would be a distinct injustice to Dr. Hicks, who, 

 notwithstanding manuscript evidence of Sir Andrew Ramsay's 

 views, was the first to draw the attention of geologists to this 

 interesting volcanic series, and to place on record a great number of 

 valuable facts concerning it. The name Pebidian should therefore, 

 in my judgment, be retained for the volcanic series of St. Davids. 



What value shall we assign to it ? On this there will doubtless 

 be difference of opinion . For ray own part I am clear that it should 

 not be removed from the Paleeozoic, that it cannot be regarded as 

 Archa3an. There remains the question : — Is it to be regarded as 

 coordinate with Cambrian, Ordovician, Silurian, or coordinate with 

 Harlech and Menevian within the limits of the Cambrian ? I incline 

 to the latter view. I am disposed to regard it as a volcanic series 

 at the base of, but not beneath, the Cambrian system. But I should 

 have no great quarrel with those who hold the other view. 



