'480 EET. J. r. BLAKE 01? THE 



contorted, but they are neither altered nor cleaved. The thin bands 

 of hard shale, with their cappings of indurated rock, often tinged 

 with iron, remind one of the Lias — the rocks are somewhat harder, 

 and I could find no fossils, but there is little further difference. The 

 direction of the crests is here somewhat reversed. 



Fig. 3. — Running of one Bed at South StacJc. 

 N.w. s:e. 



Sea-level. 



Passing to the next headland, the first rocks seen are sericitic 

 slates, and these are worked inland in close proximity to the chlo- 

 ritic schists, to which they form a striking contrast ; then succeeds 

 a series in which cleavage and foliation have gone so far as to 

 obliterate the bedding, except as seen from a distance. We can 

 trace, however, the same general S.E. dip as before, varied by 

 spaces where the contortions nm more nearly horizontally. The 

 rocks remain thoroughly bedded, when actually seen ; but, as at 

 Boscolyn, the weathering of the cleaved masses gives a uniform 

 appearance to the whole, and there is no true quartzite. Towards 

 Porth-y-corwgl the cleavage becomes less marked ; and inland, near 

 Porth-na-march, it is entirely absent, and unaltered grit is found in 

 well-marked folds *. 



These bedded rocks have, of course, a definite thickness, but it 

 would not be worth the labour to determine it accurately. I should 

 estimate it (allowing for the horizontal portions) at not more than 

 from 2000 to 3000 feet in aU. 



Sir A. Eamsay states matters quite difi'erently from all the above 

 description. He says that for three miles south of the Stack there 

 is a high dip to the l^.W., whereas I say it is to the S.E. and 

 variable. His estimate would give from 13,000 to 14,000 feet to 

 the rocks. It would seem rash to accuse Sir A. Hams ay of having 

 mistaken cleavage for bedding here ; but he makes no mention of 

 cleavage in the area, though it is certainly intense ; and there are 

 several spots where the dip inserted on the map exactly describes 

 the direction and amount of the cleavage. Perhaps the clearest of 

 these is at a promontory east of Porth Rhyffydd (see fig. 4). In any 

 case I am pretty certain of my own observations as above, and 

 cannot allow an extraordinary thickness to the series. 



* The greenstone dyke at Porth-y-corwgl, which runs near the fault, is 

 beautifully jointed both in the columnar and the spheroidal style, like the pillars 

 ixL the Griant's Causeway 



