318 T, G. BONNEY ON THE BASE OF THE 
red colour. Microscopic examination confirms this, grains of a gritty 
slate and lapilli being abundant. One or two, however, differ from 
those already described, being full of felspar microliths, partly 
grouped so as to haye a feathery or tufted aspect, and in one or two 
cases indicating an approach to spherulitic structure. Following 
the road to the north, we come to a quarry at the back of some 
white cottages (? west of Minffordd), and find a felspathic grit of a dull 
greenish colour speckled with white. Under the microscope it is 
seen to consist of rather decomposed felspar crystals (both orthoclase 
and, plagioclase recognized), varying generally from about 0’-01 to 
0”-03 in diameter, mingled with finer dust and a few small lapilli 
and quartz grains. There is a considerable quantity of viridite in 
filmy patches, looking sometimes as if it had replaced a pyroxenic 
constituent. Many fragments are little, if at all, waterworn. 
The dip over this district is often not easy to obtain with accuracy, 
but it appears to be generally not far from N.H. to H.N.H., and high. 
Returning now to the main road from Caernaryon to Bangor, which 
runs near a line of fault*, and following it towards the latter place, we 
find, after about half a mile, a quarry at the back of a cottage. Here 
we find the following ascending succession :—(1) conglomerate rather 
like that of Tair-ffynnon, with rolled fragments of red quartz-felsite, 
sometimes 4" diameter, angular fragments of purple slate, and a few 
green-coloured 2 or 3 inches diameter; (2) a fine grit, in the upper 
part not unlike one of those low down in the Llanberis Cambrian 
series ; (3) conglomerate, more slaty ; (4) a green slaty rock, near to 
which were one or two large slaty masses looking like included frag- 
ments. The section is rather irregular, and is disturbed by a fault ; 
but I believe the above to be correct, and the dip to be about 50° a 
little east of north-east. Microscopic examination of the conglomerate 
confirms the above description and the general correspondence with 
the Tair-ffynnon rock. The fragments of the quartz-felsite are very 
characteristic f. 
About a furlong further, behind another cottage, are ashy-looking 
fine grits ; and some four hundred yards from these, in a rock exposed 
behind the “ poor-house,” are greenish-grey slaty grits with a band or 
so containing felsite fragments about as large as peas. Dip nearly 
as above, but a little steeper. Microscopic examination of this shows 
various slaty and gritty fragments, lapilli, some almost wholly black 
with opacite, and the qnartz-felsite, quartz grains, &c. as usual +. 
There is one fragment of the peculiar rock observed ati Cae Seri. 
We then approach the town of Bangor and the district which has 
been fully described by Prof. Hughes, so that for the slaty beds and 
green breccias which here form the upper part of the series and 
underlie the Cambrian conglomerate (in which the characteristic 
quartz-felsite may frequently be recognized, as asserted by him and 
Dr. Hicks) I refer to his paper and my note on the microscopic 
structure of two of the rocks appended thereto. 
* The displacement hereabouts does not seem large. 
+ Across the valley on the opposite side of the fault are beds more of the 
Minffordd type. { Plate XIII. fig. 3. 
