Rev. J. F. Blahe — The Llanheris Unconformifj/. 171 



way by the road, climbing the slopes above, and also went along 

 the tram-line on the other side of Llyn Padarn from the head of 

 the lake to Llys Dinorwig. He accounts for the diiferences between 

 himself and " the officers of the Survey " by their being " occasionally 

 misled by the superficial aspect of the rocks." 



Part of this paper it is necessary to quote. Speaking of Moel 

 Tryfaen, he says: "The conglomerate contains pebbles of the same 

 purplish quartz-felsite, generally 2-4 inches diameter, but sometimes 

 a foot or more, together with angular fragments of purple slate. 

 On the western side about one-fourth of the fragments are felsite, 

 the remainder slate — green and purple, and a dull green grit 

 resembling one in the underlying series. 'The fragments of purple 

 slate are rather more numerous, on the eastern side. The strike of 

 the conglomerate appeared to be about E.N.E. and W.S.W. 

 and the bedding, as it seemed to us. dipped to the N.N.W. at a high 

 angle, but ... it was difficult to be sure of this" [Dr. Hicks 

 had made the dip N.E.]. The quartz-felsite he takes to be a lava- 

 flow, because (1) it shows flow-structure in parts ; (2) a band of 

 slate is intercalated in it and is not conspicuously altered ; (3) it is 

 associated in places with an agglomerate.^ He also gives a section 

 along the tramway by Llyn Padarn, which will be referred to 

 later on. 



One among his conclusions is that "further examination will 

 probably discover more agglomerates, and perhaps further sub- 

 divide the lava-flows," and in speaking of Moel Tryfaen, " where 

 the quartz-felsite must be very thick," says, "appearances suggest 

 that there is a marked physical break between this [the Cambrian 

 conglomerate] and the subjacent sedimentary series." 



Up to this time, therefoie, the only alternative to Sir A. Ramsay's 

 view was, that there was a single conglomerate forming the base of 

 the Cambrian, and that it lay unconformably on. or was separated 

 by, a marked physical break from the rocks below, whether felsilic 

 or sedimentary, whose fragments also its pebbles resembled : the 

 only variation being that Professor Bonney figured the conglomerate 

 in his tramway section- as conformable, but said nothing about it in 

 his text. 



In 1885 Professor Green (D) described part of this section,^ 

 which he considered to show that "the conglomerate rests 

 on these rocks with the strongest possible unconiormity." As to 

 the age of the conglomerate, he only says that it is " taken to be 

 the base of the Cambrian rocks in that district." At the reading of 



^ All these reasons seem to me to have now disappeared. We have learned that 

 flow- structure may he found also in an intrusive rock (see Sir A. Geikie in G, 

 postea, p. 93), the "slate" is a greenstone dyke, and the agglomerate may be 

 a fault breccia. Even the proof of the felsite being of earlier age than the con- 

 glomerate would not now, if that conglomerate is post-Llanberis, prove it to be 

 non -intrusive, and there remains only the fact that it is always followed, in regular 

 succession, by its own debris, or what is considered to be such, and this seems 

 sufficient. 



2 Op. cit., p. 315. 



3 Q.J.G.S., vol. xli, pp. 74-79. 



