Vol. 50.] OLDER FRAGMENTAL ROCKS IN N.W. CAERNARVONSHIRE. 589 



To this must be the final appeal. Mr. Blake maintains that by the 

 side of the slate-railway east of Llyn Padarn, his ' post-Llanberis ' 

 conglomerate can be seen unconformably overlying the beds which 

 are admittedly Cambrian. This is at the spot originally described 

 by one of us l as the second of the three masses of conglomerate 

 (numbered 3, 6, and 3, in our fig. 2, p. 590, and in our map, p. 594). 

 It is a thinner mass, as was then noticed, and it also differs some- 

 what lithologically from the first and the third, so that, from these 

 reasons, and from careful tracing of the dip in the associated beds, 

 we now incline to think this second conglomerate may be a different 

 and slightly higher band. 



In the original diagrammatic section along the railway given in 

 the description referred to above, the synclinal and the anticlinal 

 were shown. At the latter part Mr. Blake introduces a fault, and 

 we (though partly for different reasons) think that one probably is 

 present ; but we do not agree with him in thinking that " there is 

 no anticlinal" (pp. cit. p. 446). "We still adhere to the original 

 diagram, but should shift the position of the anticlinal axis in it 

 southward, so as to fall nearly on the third conglomerate ' 2 (3 in 

 fig. 2, p. 590 ; and 3, near Boat-house in map, p. 594). Again and 

 again, in the little crags just above the railway, the dips are well 

 exposed — towards a north-westerly point on the one side, towards 

 a south-easterly point on the other side of a line which is thus 

 clearly anticlinal. 



We are told, however, that the unconformity is distinctly proved 

 at one place, and it is drawn as shown in Mr. Blake's fig. 1 (op. cit. 

 p. 445). A conglomerate A lies unconformably upon the slate- 

 breccia g, and Mr. Blake states that Prof. Green, Sir A. Geikie, 3 

 and himself have recognized the difference, " which others have 

 failed to do." Even the latter statement is incorrect, for one of 

 us called special attention in 1879 to the fact that the section 

 shows conglomerate and a sort of ' rain-spot ' rock underlying the 

 conglomerate. 4 In the conglomerate, as shown in the cliff-section, 

 the pebbles are rounded or subrotund, larger, and fairly close, but 

 with a finer gritty matrix between. 5 The upper part is weathered, 

 and this causes the pebbles therein to stand out in relief, but they 

 are present equally in the lower unweathered part, the two clearly 

 forming a single mass. The underlying ' rain-spot ' rock is more 

 strongly cleaved, as stated by Sir A. Geikie. This character, however, 



1 T. G-. Bonney, ' On the Quartz-felsite and Associated Rocks at the Base of 

 the Cambrian Series in North-western Caernarvonshire,' Quart. Journ. Geol. 

 Soc. vol. xxxv. (1879) p. 309. 



2 The greater thickness of the third conglomerate might be due, partly at 

 least, to the anticlinal roll. Some, however, of the first conglomerate might 

 be cut out by the fault which limits it on the south. 



3 Sir A. G-eikie, however, does not admit the existence of the unconformity. 

 Quart. Journ. Greol.Soc. vol. xlvii. (1891) Pres. Addr. Proc. p. 95, note. 



4 'A sort of 'rain-spot' rock at the base of the middle mass,' T. G. Bonney, 

 op. supra cit. p. 315. 



3 The pebbles are not unusually 1^" or 2" long by 1|" broad, but most 

 commonly from £" to §". In the 'rain-spot' rock the fragments are 

 smaller and more elongated along the cleavage. 



