280 PEOF. J. p. BLAKE OX THE CAMBEIAN 



in the sequence, some more halleflintoid rock (well shown in a 

 quarry by the roadside), and we must go to the east again to find 

 the conglomerate of large stones in the nearest spot of the adjacent 

 field. This can scarcely be brought about by a fault, since the 

 Arenig is undisturbed ; and moreover the coarse grit does not 

 resemble the conglomerate, but resembles more closely a grit seen 

 where its continuation should be, to the west of the conglomerate on 

 Bryniau Bangor. The great conglomerate appears to die out on the 

 south, as conglomerates do ; but we may trace it from a knob at about 

 the " n" of Bryniau, in a north-north-west direction, to the west of, 

 and nearly parallel to, the road ; and this strike leads exactly to the 

 spot where it is found in the road, as noticed by Prof. Hughes. It 

 is therefore strictly conformable to the underlying beds. It is just 

 near its southern termination, but on the opposite side of the road, 

 that the escarpment of Arenig grit is seen striking N.X.E., in other 

 words making an angle of 45° between the two. There is there- 

 fore no conformity with the overlying beds. Moreover, if the great 

 conglomerate were the base of a new series, the beds above ought 

 to be decidedly different. There are certainly a few purple beds in 

 the road, but so there are far away to the south; but the main 

 mass is difficult to distinguish from the halleflinta below — so difli- 

 cult, it appears, that Prof. Bonney, by curving round the conglo- 

 merate, has made beds, which really lie above it, appear to lie heloiv^ 

 thereby unconsciously testifying to their identity. 



I can therefore regard this so-called hasal Cambrian conglomerate 

 as nothing else than another and the most remarkable of the series 

 of conglomerates which characterize these " Bangor beds." It is 

 clear, then, that above the porphyry we have an ascending con- 

 formable series of conglomerates, grits, and more or less banded 

 halleflintas, alternating with each other and overlapped uncon- 

 formably along their eastern side by the Arenig grit. 



I have also carefully examined the country on the western side 

 of the fault, but I am afraid it is more or less labour lost : we learn 

 nothing further as to the succession, and cannot hope to tell whether 

 a rock is conformable or not, especially when, like the great con- 

 glomerate, it changes its strike by more than 45" in the course of 

 its 1\ mile run. But I am not in the least certain that this is on 

 the same horizon as the great conglomerate on the other side of the 

 valley. To begin with, the pebbles are not the same, those on the 

 east being far more quartzose ; but the rock is most like one of the 

 beds at Tairffynon and the dark conglomerate of Pachell, a corre- 

 lation made by Prof. Hughes. It would require the least number 

 of faults to bring this about, and the beds actually seen below it are 

 similar to those which occur below the Tairffynon conglomerate, 

 while the beds above are more comparable on the two sides of the 

 valley than they would be if we identified it with the conglomerate 

 of Bryniau Bangor. I think the vno^t prohahle stratigraphy here 

 would be to draw a line of fault with an upthrow on the east, 

 making a very small angle with the main fault, and running from 

 near the " Inn,'' opposite Treborth, to beyond the Baths at Garth, 



