516 EEV. J. p. BLAKE ON THE 



to be no reason why fossils should not occur, since no cleavage exists. 

 This undisturbed state is continued as far as Amlwch, to the east 

 of which wonderful contortions set in. That they are the same 

 set of rocks which we find contorted on the east, and have been 

 tracing uncontorted from the west, is seen from the fact that they 

 are continuous on the strike, that there are a few spots on the 

 west where similar contortions occur, and a few on the east where 

 they are uncontorted, as for instance at Tal-drws, and that we can 

 see the contortions gradually set in by tracing the rocks along 

 the coast. I think these contortions afford a proof that the 

 bounding fault is a push-fault and not a slip-fault ; for in the 

 latter case what is there to develop them more at this spot than 

 any other ? but in the former, if the thrust took place after the 

 extrusion of the felsites of Parys Mountain, as it certainly did 

 after the granitic outburst further east, these would afford a buttress 

 against which the rocks could only be contorted, since they could 

 not bodily move, while further west the soft Ordovician shales 

 would offer no resistance ; and it may be noted that the cross-fault 

 which breaks the main one runs exactly on the boundary of the 

 contorted and uncontorted portions. 



Sir A. Ramsay is at great pains to show that foliation is here de- 

 veloped obliquely to the bedding. Unfortunately an examination 

 of the ground leads to the conviction that he has taken the cracks 

 which are naturally produced along the crests of the folds for the last 

 relics of bedding, and the banding of the rock for foliation. These 

 folds may be traced from mere undulations to sharp, and then to 

 broken, contortions ; and, strictly speaking, the rocks are not foliated 

 at all ; they are only banded slates in which some alteration by the 

 development of flakes of sericite has taken place. There is a con- 

 siderable variation in the fineness of the material. It is only where 

 it is coarser, as at Crogan Goch, that cracks are produced. Where it 

 is finer, like that which produces the marbled slate, the contortions 

 produce a most beautiful damascened pattern, without a trace of 

 cracking, as at the junction of the roads near Ty Xewydd. Any 

 such bedding as Sir A. Ramsay supposes would, moreover, be quite 

 irreconcilable with the surrounding stratigraphy. 



Towards Llaneilian and Point ^lianus still coarser beds set in 

 on the same strike, and are well exposed on aU the cliffs of this 

 sea-torn promontory. These are practically ashes, since they contain 

 angular fragments of quartz and felspar in a much finer matrix, in 

 which also there is abundant sericite. The supposed cross-foliation 

 here described by Sir A. Ramsay is very evident on the ground ; 

 but when a sample of the rock exhibiting it is examined microscopi- 

 cally, it is seen that the supposed lines of foliation are, in reality, 

 well-marked secondary cracks in which a distinct formation of 

 Rfiricite has taken place, but which in no respect interfere with 

 the structure of the intervening substance. True foliation is only 

 general in the lower part of the series round Mynydd Mechell ; in 

 all the rest there is but one type of material, in which sedimentary 



