ANGLESEY AND CAERNARVONSHIRE. Oe 
Pebidian (Bangor) beds are also plentiful, and it is interesting to 
note that here, as in South Wales, the porcellanites of that series are 
found in exactly the same condition in which they now occur in 
the beds in the neighbourhood. This, to my mind, proves conclu- 
sively that the change in the Pebidian rocks had taken place to the 
extent now observed before the basal Cambrian conglomerates were 
deposited upon the Pebidian rocks, as these porcellanites are un- 
doubtedly rocks of detrital, and not of volcanic origin. Specimens 
Nos. 13 and 14, described by Prof. Bonney (p. 205), are from the 
conglomerates on the shore of the Menai Straits, south of Garth 
Ferry, and they are interesting in showing that the spherulitic 
quartz-porphyries here, as at St. David’s, formed a part of the Pre- 
Cambrian ridge*. I did not happen to meet with any typical 
fragments of the Dimetian at Bangor, but in the conglomerates 
at Dinas Dinorwig, east of Llanddeiniolen (see Section, fig. 2), 
which is about halfway between Bangor and Caernarvon, I was 
fortunate enough to meet with many pebbles of most typical Dimetian. 
These conglomerates are mentioned by Sir A. Ramsay as among the 
lowest Cambrian beds of the district, therefore the evidence of their 
position is not disputed. Two of these pebbles, Nos. 10 and 11, are 
described by Prof. Bonney (p. 204). The other fragments in 
this conglomerate are mainly quartz-felsites as at Llanddeiniolen, 
where they rest directly on the quartz-felsites (Dinorwig beds of 
Prof. Hughes). In the Cambrian conglomerates, about a mile 
further south, on the road to Pont Rothell, I also found fragments 
of the typical Twt Hill (Dimetian) rock (no. 9, p. 203), and the 
associated fragments were again like those of Dinas Dinorwig and 
Llanddeiniolen. The Cambrian conglomerates on both sides of the 
quartz-felsites of Llyn Padarn were described in my former paper, and 
specimens deposited in the Society’s Museum. Further examination 
of these conglomerates has proved conclusively, as I had previously 
stated, that they are mainly derived from the quartz-felsite ridge. I 
examined the conglomerates at Bettws-Garmon, about four miles 
south of Llyn Padarn, on the east side of the ridge, and here also the 
pebbles were mainly quartz-felsites and fragments of Pebidian rocks. 
i also reexamined the great conglomerate at Moel Tryfaen, and in 
this I found bits of Dimetian as well as the usual fragments which 
have been described as characteristic of this basal conglomerate. 
The masses of Pebidian rocks in this conglomerate are very large, 
some of the porcellanites being from 8 to 10 inches across. The felsite 
pebbles are also of large size. This conglomerate is undoubtedly the 
* Tn the discussion on Prof. Geikie’s paper Mr. T. Davies mentioned that large 
pebbles of the well-known spherulitic quartz-felsite exposed in the Church-school 
quarry at St David’s occurred in the specimen of the Cambrian conglomerate 
which I had some years previously presented to the British Museum. ‘These 
quartz-felsites at St. David’s are stated by Prof. Geikie in his paper to be peri- 
pheral quartz-porphyries to what he callsthe mass of intrusive granite (Dimetian), 
and are therefore claimed to be very much newer than the Cambrian conglo- 
merates, which actually contain the rolled fragments of the rocks themselves ! 
T Prof. Bonney has described in a previous papera fragment of Dimetian from 
the Llyn Padarn Conglomerate. See Quart. Journ. Geol. Soc. vol. xxxv. p. 316. 
* 
