Yol. 56.] GEOLOGY OF NORTH KRX ANGLESEY. 239 



they are followed by the Trwyn y Pare Limestone. In much of 

 this limestone the bedding cannot be made out, in parts it is a 

 recemented breccia. The section shows that the limestone is under- 

 lain by the authiclastic rocks of Trwyn y Pare. Though the change 

 from grits and slates to limestone is abrupt, and the junction in places 

 is certainly one of movement, the conclusion is inevitable that 

 the Trwyn y Pare Limestone succeeds the Trwyn y Pare Grits and 

 Slates. A passage between the two can be seen along the course of 

 the rifle-range in Cemaes Bay. 



The parallel sections (see PI. XIV, fig. 1) show how greatly the 

 details vary at short intervals along the line of strike. 



On reaching the southern cove of Porth Padrig a marked 

 change is observed in the rocks, introduced apparently by a fault. 

 Pale quartzites and quartzose grits are now the characteristic 

 feature, interbedded with gritty shales, some with broken-up grit- 

 bands. The quartzites are either flaggy and well-bedded with shaly 

 partings, or massive and obscurely bedded, though exhibiting clastic 

 grains. The gritty beds vary in colour, being light grey, greenish- 

 grey, blue-grey, sage-green, and yellowish, and some of them are 

 crushed to fine i augen '-grits. In this group also occurs a rotten 

 ferruginous rock, which has been worked for umber. There is 

 moreover some limestone, one mass lying between tide-marks, and 

 another mass appearing in the cliff. This latter overlies a ' crush- 

 conglomerate/ from which it is separated by an anticlinal curve, as 

 shown in the section (PI. XIV, fig. 1 ). 



The faulted patch of Llandeilo Shales mentioned on p. 237 

 now intervenes, beyond which reappear the quartzites with their 

 associated shaly rocks. They form the northern part of Porth 

 Padrig, where they were once worked for ' china-stone.' 



The rocks of Porth Padrig are so much broken that their 

 structure and relationships cannot be made out with any certainty, 

 but they appear to be part of a shattered synclinal fold, the core of 

 which is represented by the graptolitic shales. Thus they may 

 be provisionally considered to belong to a higher horizon than 

 the Trwyn y Pare Limestone. Beds of much the same character occur 

 in the south of Porth Wen Bay, where they similarly appear to belong 

 to a higher zone than the limestone formerly quarried there. 



Section 2. — This section (PI. XIV) is drawn in a north-easterly 

 direction through the broken rocks at Llanbadrig, and is practically 

 a continuation to the north-east of Section 1. The quartzite at 

 Llanbadrig Point has been previously described. 1 The succeeding 

 beds are mostly crushed shales and slates, so shattered that the 

 contorted character of the whole is much obscured, though occasion- 

 ally revealed. They include some broken-up bands of grit and 

 quartzite, and are more shaly than the rocks at Trwyn y Pare ; but , 

 like the latter, they pass up into a limestone, which towards Llan- 

 badrig Church contains black shale of a character similar to that 

 occurring in the limestone of Trwyn y Pare Quarry. The coast- 



1 Quart. Journ. Geol. Soe. vol. Iv (1899) p. 653. 



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