250 



KEV. J. F. liLAKE ON THE EOCKS MAPPED AS 



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lets in the Upper Slates. The same 

 grit is met with on the west side of 

 the Penrhyn Quarries, where it forms 

 a ridge which appears to die out at 

 the north-eastern end and to be cut off 

 at the other hy the great fault that 

 shifts the Bronllwyd Grit. The greater 

 part of the slates to the west are a 

 repetition of the Upper Slates, as is 

 shown by the Bronllwyd Grit over- 

 lying them at Glan-y-gors and by the 

 occurrence in them of the upper thin 

 band of grit at Felin Pawr slate-works, 

 which is followed below by the St. 

 Ann's Grit. 



AVe cannot be sure that all the other 

 grits referred to the St. Ann's Grit are 

 exactly on the same horizon : all we 

 know of them is that they have ap- 

 proximately the same character, are 

 very massive, and lie in the midst of 

 the Purple Slates. Such a mass covers 

 the eastern slope of Pare Drysgol, 

 and, having very much the same dip 

 (see fig. 5) as the fall of the ground, 

 appears to be more important than it 

 probably is. Nothing but grit, how- 

 ever, can be found on this slope, so 

 that there are not two or three bands, 

 as marked on the Survey map. To the 

 west of it comes the Lower Purple 

 Slate. All this lies on the western 

 side of the above-mentioned fault, so 

 that the Drysgol grit is the continua- 

 tion of the St. Ann's. On the eastern 

 side of the same fault we find the Careg 

 Ludan grit, which occupies approxi- 

 mately the same horizon, but has a 

 more bedded character and is not quite 

 so green. It is thrown into a sharp 

 synclinal at the slate quarry called 

 Chwarel Fawr, Dinorwig, where the 

 Lower Slates have been worked and 

 the grit is seen forming an arch above 

 them. The northern limb of this arch 

 is found between this quarry and the 

 felsite of Moel Gronw, while the 

 southern spreads out on the broad slopes 

 of Careg Ludan, which, coinciding 

 somewhat with the surface of the fold. 



