ROCKS IN N.W. CA-ERNARVOKSHIRE. 279 



still, with lines curving about almost like a vitreous lava, but actually 

 a hiilleflinta. The beds above are breccias, and finally a green-banded 

 rock again. We seem to have here, in miniature, the whole series 

 as seen further north near Bangor, but this may not be so really. 

 The red felsite-conglomerate, indeed, appears to die out, no trace of 

 it appearing in the fields a little to the north as we walk across the 

 strike of the series. 



Seen under the microscope, Nos. 2, 5, 6, 7, seem all of the same 

 type, the fragments in the several rocks dift'eriug only in size. Most 

 of them are mineral fragments, but there are some characteristic 

 rock fragments of a basaltic type, consisting of long transparent 

 crystals scattered irregularly in a black opaque ground-mass. I 

 know of no rock in this district, except in Anglesey, from which 

 such fragments could be derived. The red felsites in No. 4 are very 

 like those below ; but one fragment I take to be an altered pumice, 

 since it contains long cavities drawn out into fantastic shapes, and 

 lined by a coat of inward-growing crystals ; if such is its nature, it 

 no doubt formed the surface of the felsites. 



Passing north we come to the region so carefully examined by 

 Prof. Bonney. I have, I trust, examined it with equal care, and 

 can fully confirm the accuracy of his observations, particularly in 

 those points in which he differs from Prof. Hughes. I have traced 

 the quartz-felsite grit by Ehos fawr, Brithdir, round by Wern into 

 the valley, where it curves westward round the edge of the felsite. 

 Then the green laminated beds on the summit of the hills, and the 

 porcellanites by Penhower, as far as the commencement of the Tair- 

 ffynon lane; then the great agglomerates, jasper conglomerates, 

 and grits at Tair-ffynon, and the quarry by the side of the main 

 road, where, however, the dip is turned round, probably in the 

 neighbourhood of the fault ; then the finer beds at Perfeddgoed, 

 which include a quantity of purple slate, near Caer-hun and to the 

 north of it ; then a bluish breccia at the corner south of Cae Seri, 

 which may be well matched at the poor-house, and another to the 

 north, which may or may not be the same as that at Hendrewen ; 

 and finally the great halleflintoid mass which, commencing with 

 Mniffordd and J^ant Gwtherin, forms the western slopes of Bryniau 

 Bangor. I have nothing to add in this region to the proofs adduced 

 by Prof. Bonney in support of his statements of the succession, which, 

 to those who have examined the ground, should be perfectly con- 

 vincing. (See the Map, fig. 1.) 



Here, however, we part company. There lies to the north a 

 conglomerate of large stones which, for some reason T have never 

 discovered, has been called by everyone in latter days the basal 

 Cambrian conglomerate. Now the last few of the grits having 

 had a pretty persistent strike of N.N.W., we find in the fields 

 by Nant Gwtherin another coarse grit, its strike still N.N.W. 

 This seems to have been identified with the so-called " Cambrian 

 conglomerate " by Prof. Hughes ; but a careful survey will show 

 that this cannot be right, for we can follow this grit for some dis- 

 tance along its strike, and find to the east of it, i. e. above it, 



