116 a. D. Roberts — The Twt-HlU Conglomerate. 



the meeting of the Society. It will be in the recollection of all 

 who were present at the meeting of the Society that in the original 

 diagram Twt Hill was shown on the left, the beds dipping towards 

 it. This indication of the direction was omitted in the published 

 section, which section did, however, represent the general appearance 

 of the face of the quarry with the oblique patches of conglomerate 

 inclined along the surface of the granitoidite towards Twt Hill. 

 After this direction of dip was given up it was still held by some 

 that the trend of the rocks was across the ridge of the Bangor- 

 Carnarvon range, until in the footnote to a paper (Geol. Mag. 

 Vol. VII. p. 300) Prof. Bonney stated that he had, as the result of 

 subsequent examination, inferred that the trend of the beds in ques- 

 tion corresponded more nearly, than he was formerly inclined to 

 believe, with the line of the ridges, and that the Careg Goch grits, 

 which he had believed dipped towards Twt Hill so as to pass 

 under the Twt Hill conglomerate, might not in reality be at a 

 lower horizon than that conglomerate. Now, however, he is so far 

 persuaded that these grits are the same as the Twt Hill con- 

 glomerate, that, from having found felsite fragments in them, he is 

 prepared to admit that the Twt Hill conglomerate is not a part of 

 the granitoidite series. It might not be apparent to those who have 

 not the map before them that the grits referred to as near the C 

 of Cefn Cynryg are the same as those previously described as the 

 Careg Goch grits, which are quarried within a stone's throw of the 

 farm of that name, Cefn Cynryg farm being on different beds away 

 to the south-east. Furthermore, the italicized portions above quoted 

 render it perfectly clear that Prof. Bonney's section was taken along 

 the line A B, since, in the section seen along C D, the conglomerate 

 passes up into a sandstone, and not into any rock which could be 

 spoken of as having " some resemblance to the bottom rock," i.e. to 

 the granitoidite. The W.S.W. side of the quarry has always been 

 much covered with brambles and debris, so that the succession was 

 not obvious at first sight, and the patches of conglomerate clinging 

 to the face of the granitoidite in irregularly oblique bands might 

 easily appear, at a little distance, to be interstratified with it. 



Prof. Hughes's section (Fig. 3), which represents the real sequence 



Fig. 3. Line of Prof. Hughes' section (Cto D. See Ground Plan, Fig. 1). 

 SSE y"'^^^"^^"^--^ NNW 



of the beds, was along C D, and is given in his paper, Q. J. G. S. 

 vol. XXXV. p. 683, containing the detailed stratigraphical evidence 

 upon which his conclusions were based. The view of the Cambrian 

 age of the conglomerate was strenuously opposed by Prof. Bonney 



