584 l'KOP. T. G. BONNET AND MISS C. A. RAISIN ON [Nov. 1 894, 



followed by two or three still thinner, — a sequence which commonly 

 happens. 



Thus we maintain the ' opposite conclusion,' to quote Mr. Blake's 

 own words, 1 and although we deny the identity of b with the Purple 

 Slate, we do not ' miss the synclinal,' but make it more definite ; 

 and we fail to see any reason why m at least should not be faulted up. 



Tracing the beds inland, the last-mentioned faults would account 

 for the difference of the rocks exposed in the grounds opposite 

 Glyn Padarn. Our observations there do not accord with Mr. Blake's. 

 We are told that we come to grits and conglomerates which are 

 ' corresponding rocks ' 2 to those of the railway-section. The con- 

 glomerate m is the massive quartz-felsite conglomerate with 

 quartzite-pebbles (3 in fig. 4, map, p. 594) ; but the conglomerates 

 or pebbly bands (in the grounds) and the associated grits are, many 

 of them, quartzose rocks containing quartz-pebbles and grains of 

 blue quartz (11 in fig. 4, map, p. 594). This rock is similar, there- 

 fore, in many respects to the green grit with blue quartz associated 

 with the Purple Slates 3 ; and in these very masses layers of purple 

 slate or argillite occur. Even the "large mass of purple slate 

 lying horizontally on the top of finer conglomerate " 4 seemed to us, 

 if we correctly identify the place, to belong certainly to one of 

 these bands. It is not, therefore, a fragment derived from any 

 possible underlying rocks, and so no proof that the series is ' post- 

 Llanberis ' in age. 



Mr. Blake says : " If we pass along an E.N.E. to W.S.W. line 

 ... we cross a definite succession." It is not easy to recognize this 

 definite succession. Compact grits are followed by a coarse green 

 pebbly grit with bands of conglomerate and of argillite, but beyond 

 the wall this runs on the west right up to the slate tips ; the grey 

 slate outcrop being nearer the quarry. It is further stated that 

 this succession has " a gentle dip towards the E.N.E." and that 

 " we have here a series .... nearly horizontal." Some of the 

 dips which we noticed are obscure, but three are clear : — to N.N.W., 

 to N.W., and to N. of W. at 30°, 18°, and 30° ; while one dip to 

 S.E. at 32° appears to be due to a synclinal roll. 



The description of a regular series takes no account of any 

 faults, but one at least (probably two) can be traced across the 

 neighbouring slate-quarry. 5 The apparent interruption of this slate 

 may be due to another line of fault roughly north-easterly, for, as 

 we have stated, a fault is seen (or rather parallel faults) on the 

 railway-section near the continuation of the line of junction. 6 



1 Op. cit. p. 452. 2 Ibid. p. 453. 



3 A green grit, containing similarly blue, purple, and red quartz-grains, is 

 characteristic of certain bands in the Harlech and Barmouth areas. 



4 Ibid. p. 453. 



B This may be partly the cause of some variation in the dips and outcrops 

 nearer the road. 



6 These are shown in the section given by Mr. Maw (G-eol. Mag. 1868, pi. vi. 

 and p. 121), from which our drawing differs in some minor details. We have 

 not, however, thought it necessary to give a separate diagram, as we believe 

 that Mr. Maw's drawing correctly represents the important points of the 

 general succession, except in the matter of the unconformity. 



