314 T, G. BONNEY ON THE BASE OF THE 
of the ground-mass is more glassy, and there are some indications 
of flow-brecciation. I may also refer to a specimen from Lland- 
deiniolen, described by me in an appendix to Prof. Hughes’s paper *, 
which belongs to the same series. I was then wholly ignorant of 
the relations of the rock to the others in the district, and had formed 
no opinion about them, as [ had never examined the felsite a situ, 
and so venture to quote the remark which I made on the appear- 
ance of the slide :—‘ The rock is probably from an old flow of rhyo- 
litic lava.” 
Thus, although in one place the top of the quartz-felsite, where it 
is most affected by subsequent pressure, does bear something of a 
schistose and fragmentary character, and though doubtless old com- 
pact felsites are sometimes very difficult to distinguish from certain 
rocks of similar chemical composition, but of sedimentary origin, I 
think we are justified in saying that the evidence against the theory 
of metamorphism is too strong to be resisted=. If; however, further 
proof be needed we shall find it in the overlying series of slaty and 
conglomeratic rocks. 
These then we proceed to examine, commencing with the south- 
western side of Llyn Padarn. Beyond the cutting in quartz-felsite 
(No. 4), the railway crosses a small bay of the lake, and then passes 
into fine green grits or “bastard slate,” beyond which we find a 
thick mass of interbedded conglomerate and similar grit, then 
another band of the grit, followed by a band of small rolled frag- 
ments of felsite about as large as hemp-seed. As, however, this 
section has been carefully drawn by Mr. Maw$, and more than once 
described ||, I will confine myself to microscopic details, merely 
stating that we endeavoured to trace the junction of the felsite and 
overlying rocks near the highroad. It is, however, much masked 
by débris and vegetation ; but there is lttle doubt there is a fault, 
through which a greenstone dyke has subsequently forced its way, 
and which has cut out some of the grits visible by the shore of the 
lake. Near the road the felsite and conglomerate are seen on 
* Vol. xxxiy. p. 145. I have recently visited this locality and examined the 
felsite, which is rather pale in colour, but not otherwise remarkable. I also 
visited several other felsite exposures in the district, which present differences 
only yarietal, though in some cases possibly interesting. 
+ I should perhaps mention that, to my mind, there is nothing to connect 
this local crushing with any theory of volcanic activity. I have observed in 
Wales several cases of this crushing of the exterior portion of a compact igneous 
rock, so that it assumes a sedimentary or schistose aspect. 
{ These rocks haye a certain resemblance to some of the lavas from the 
Wrekin district described by Mr. Allport (Quart. Journ. Geol. Soc. vol. xxxiii. 
. 449), also, to a less extent, to some of the fragments in the Charnwood agglo- 
merates. They differ considerably from the felsites in the Bala series of Northern 
Caernarvonshire. 
§ Geol. Mag. vol. v. pl. 6. 
|| Geol. Mag. vol vy. p. 121, where some analyses of neighbouring rocks are 
given; also Quart. Journ. Geol. Soc. vol. xxxiy. pp. 148, 150, 764; Mem. Geol. 
Survey, vol. iii. p. 142. I may state that I carefully examined the “uncon- 
formity” asserted by Mr. Maw to occur in the railway-cutting higher up, and 
have no hesitation in agreeing with Prof. Hughes, and so differing from Mr. 
Maw, in his interpretation of the phenomena. 
