VOLCANIC SERIES OF ST. DAYIDS. 259 



place north of Ogof Golchfa, by which Menevian beds, as determined 

 by Dr. Hicks, are brought down so as nearly or quite to abut 

 on Pebidian, The other faults, though their effects are sometiraes 

 well marked, as at the Ogof Goch, (Jarn-ar-wig, and north of Perth 

 gele, are of no great magnitude or importance. A glance at the 

 map will show that the Caerfai beds (e. g. to the west of Perth Sele, 

 and in the neighbourhood of Castell) are affected by faulting to 

 as great an extent as the Pebidians which underlie them. In fact I 

 failed to find any evidence of faulting special to the Pebidian, as 

 opposed to the other Cambrian strata. 



e. The Cambrian Overlap. — I have before stated that neither iu 

 Caerbwdy valley, in St. Non's Bay, nor at Ogof Golchfa, did I find 

 satisfactory evidence for the overlap marked on Dr. Hicks's maps 

 and plans. There is such erosion as is inevitable from the nature 

 of the conditions under which the conglomerate was formed. More 

 than this I failed to see. 



Dr. Hicks, however, contends that between P,hoson and the 

 exposure of the conglomerate on the coast-line beyond Perth Sele, 

 "the facts prove that in this mile of country a quarter of a mile in 

 thickness of nearly vertical Pedidian strata has been overlapped by 

 the conglomerates." 



The facts are these. Near Maen Bachau, south of Castell, the 

 conglomerate is seen on the coast-line. Then it is occasionally seen 

 in the faulted ground between this locality and Rhoson, where it is 

 seen striking N.E. with a low dip. The underlying Pebidians at 

 Rhoson are not " nearly vertical," but have also a low dip and a 

 strike similar to that of the conglomerate. There is, then, no 

 exposure of the conglomerate till it is seen in the field inland and 

 to the east of Porth Sele, where its strike is iN^. 15° E. Here it has 

 been displaced 175 yards by the fault before alluded to, on the north 

 side of which it occupies the coast-line, with a strike iS^. 35° E. 

 The faults between Maen Bachau and Rhoson and this fault are 

 step-faults constantly throwing the beds to the jN'.E. The proba- 

 bilities are that it is by step-faults between Rhoson and Perth Sele, 

 and not by overlap, that the displacement of the conglomerate has 

 been effected, and this view is borne out by the evidence of faulting 

 west of Porth Sele and near Porth Stinian (see map). In any case 

 it is incorrect (1) to speak of nearly vertical Pebidian, and (2) to 

 neglect the probable effects of faulting. 



But it may be said that the evidence of overlap is not merely a 

 matter of the strike of the beds, it is the fact that the conglomerate 

 is found resting upon diff'erent beds of the l^cbidian series. Here 

 again Dr. Hicks's map is misleading. Through missing the fault at 

 Ogof Goch he makes the conglomerate rest upon his C group of 

 quartz-felsite breccia and sheets. It does not do so. It is faulted 

 against them. Even if this piece of evidence be eliminated, however, 

 we have the unquestionable fact that at Ogof (iolchfa the conglom- 

 erate is resting upon schistose sedimentary-looking beds, at Maen 

 Bachau it is in close proximity to " diabase " lava-flows, and at 



