586 PKOF. T. G. BONNET AND MISS C. A. EAISIN ON [Nov. l8g4> 



suspicions that they were not what they had been taken for." 

 In an area extending for about | mile "above the road from the 

 Olyn Peris Hotel to the commencement of the felsite,' passing 

 Tan-y-pant, some roughly horizontal outcrops occur, 2 but fourteen 

 dips more or less trustworthy were measured, out of which not 

 one was horizontal, very few were gentle dips, the average was 

 from 30° to 35° or 40°, and two at least indicated high angles ot 

 50° and 70°. 3 ... 



We have not worked over all the details farther up the hill, dim 

 until some distinction is drawn between different grits and con- 

 glomerates no inference from isolated outcrops can be trusted. 

 Certainly the specimens at one part from near Cefn Du quarries, 

 lithologically, are similar to the quartz-grits which are found among 

 the workable slates, and are very different from the great quartz- 

 felsite conglomerate. If slate-holes were found on different sides ol 

 this grit, 4 this would be no more than might have been anticipated. 



IV. East op Llyn Padakn : Inland Sections. 



Along the eastern boundary of the series of conglomerates, etc., 

 Mr. Blake's map is misleading, even according to his own descrip- 

 tion. As he says, the conglomerate i resembles a, yet he marks it 

 by a different symbol (op. cit. p. 447, fig. 2). It is with this con- 

 glomerate, i (3, near the Boat-house, in our map, p. 594), that w e 

 have to correlate various outcrops north of Mr. Blake's 18, west of th® 

 felsite on which 24 is marked, while the so-called ' Banded Slates 

 (g-h, op. cit. fig. 2, ' Cambrian ') are many of them lithologically 

 indistinguishable from — and can be traced along to — the banded 

 gritty series of the east of Y Bigl marked as ' post-Llanheris ' (see 

 our map, 5, 6, 7, p. 594). 



A further argument is based on the stratigraphy of Moel Goronwy 

 (Moel Gronw). Mr. Blake states that the felsite of this hill differs 

 from that of Clegyr in being more compact. 5 We think it would be 

 an improvement to substitute ' less ' for ' more,' but the difference 

 is trifling and the former rock agrees in its general character 6 with 

 the ordinary felstones of the neighbourhood, displaying a fluxional 



1 Op. supra cit. p. 455. It is impossible, we find, to be sure of the exact 

 outcrops indicated by the numbers on Mr. Blake's maps ■ but the area examined 

 here extended beyond ' 18, 16, 10,' the points to which he especially referred. 



- At some spots small synclinals or anticlinals seem indicated. 



3 Other dips not so well exposed were measured, and many more were 

 noticed. Some variation in the dips doubtless is due to the intrusive greenstone. 

 The whole hill very possibly is underlain by a large mass, which may occur 

 like a laccolite, and certain of the strata are baked and changed to porcellanite. 

 Some knobs of hard purple slate occur, which evidently are parts of the banded 

 series altered in this way. The general dip in the part towards the felsite is 

 to a north-westerly point, but south of the Tan-y-pant streamlet the direction 

 is changed. 



4 Op. cit. p. 455. 5 Ibid. p. 450. 



6 One slide of the rock includes many small crystals of secondary minerals, 

 some being white mica, others probably a carbonate. But similar minerals 

 occur in the main mass of the felsite. 



