Vol. 55.] THE GEOLOGY OP NORTHEKS- ANGLESEY. 663 



around Cemlyn Bay. The matrix is also comparable with the fine- 

 grained beds of the same series. I consider that the strata are, in the 

 main, the upper beds of the Green-and-Purple Series, the grit-bands 

 of which have been so much broken up that the fragments lie piece- 

 meal in the shaly matrix, though contorted bedding can still be 

 traced in places. As for the quartzites and limestones, some of the 

 former are green, and graduate into the ordinary green grits, and 

 such may, therefore, be considered altered grits of the same series ; 

 but others, and the limestones, are in all probability parts of beds 

 occurring higher in the succession, which have been folded in and 

 crushed among the older disrupted strata. 



As we pass along the shore, between Perth yr Ogof and Perth y 

 Wyifa, the crush-conglomerates still resemble the Cemlyn beds, and 

 the grit-bands can be traced here in places, though generally they 

 are completely disrupted. At the south-eastern corner of Perth y 

 Wylfa, the greyish-green slates and flaggy grits of Perth y Pistyll and 

 Perth y Gwartheg reappear. Some of the grits are broken to 

 crush-breccias, but the fragments are angular and little displaced. 

 To the north authiclasts again appear in the rocks, and this pseudo- 

 pebbly character obtains along the coast all the way to Cemaes. I 

 have not noticed any of the felsite-fragments which have been 

 stated to occur both here and on Mynydd Wylfa. On Trwyn y 

 Penrhyn (near Cemaes village) the rocky coast exhibits, among the 

 broken-up grits and slates, masses of quartzite and limestone, some 

 over 300 feet long, which follow the general strike of the beds. 

 The limestones are clearly identical with those that occur on the 

 eastern side of Cemaes Bay, where they are more fully exposed. 

 Some of the calcareous shales belonging to them are also disrupted. 

 I give a section (fig. 9, p. 660) along this part of the crush-zone which 

 shows that in general structure the crushed rocks consist of a series 

 of overf olds. This section (taken obliquely to the strike of the beds) 

 gives only a generalized suggestion of what has taken place ; the 

 folding is in reality very much more complex, and is complicated by 

 numerous thrusts and faults. In one spot, opposite the house 

 known as Bay Yiew, where the flaggy beds which constitute the 

 bulk of the crush-conglomerate have been less disrupted than usual, 

 the folding is still evident (fig. 10, p. 662). 



The eastern shore of Cemaes Bay yields further exposures of 

 crush-conglomerate. Near the rifle-range is seen bedded limestone, 

 passing down into glossy blue-black and greenish shale and beds 

 of quartz-grit and quartzite. The bedding is very irregular; 

 the bands of grit and quartzite are squeezed out among the shales 

 into a succession of somewhat lenticular or rounded pieces, and 

 all gradations from long bands to isolated fragments and lumps 

 may be noticed. Fig. 11 (p. 664) gives an example of two such bands 

 from this locality. These irregular crumpled beds of grit, quartzite, 

 limestone, and shale are to be seen as far as the target which 

 is fixed upon a headland (Pig y Barcud) of highly-contorted lime- 

 stone and laminated limestone-shale. Occupying a broken and 

 overf olded anticline between this limestone-headland and the large 

 limestone-quarry of Trwyn y Pare is a strip some 100 yards wide 



