690 PROF. T. M‘KENNY HUGHES ON THE PRE-CAMBRIAN 
It is not, however, found to be so much decomposed as we 
follow it towards Caernarvon. In the quarry at Hendrewen, where 
Fig. 9.—Section from road near Glan Adda, x mile S.W. of Bangor 
Station, due E. across Bryniau. (Length of Section 1 mile.) 
W. E. 
Road 8. of 1 mile W. of 
Bangor station. Hendrewen. Llandegai. 
a*. Black and grey banded flaggy shales. 
a?. Sandstones and grits. Cambrian. 
a. Conglomerate. 
B. Volcanic series, Bangor beds. d, Dyke. 
it is seen to be dropped by a small fault against the Bangor beds to 
the N.W. flank of the Bryniau ridge, it consists of a very tough 
grit and irregular conglomerate, the conglomerate in places being 
very coarse ; one pebble was over a foot in longest diameter. It is 
here traversed by a dyke, near which it is slightly altered. These 
beds can be followed, dipping in a N. and N.W. direction, to near 
Tairffynnon, W. of which place the Bangor beds crop out below 
them. ‘They can be traced along the N. side of the valley towards 
Perfeddgoed, and crossing the valley, which probably coincides with 
faulted ground, we can trace similar purplish conglomerate and 
grit up the road to Wern, and here and there E. of Brithdir, across 
the road N.E. of Cae Cerig, and beyond the rough land of Rhosfawr. 
We find bosses of grey coarse grit on one side and of felsite on the 
other over the hill to Fachell. There we have a fine series of 
sections, from which the E.N.E. part of fig. 6 has been drawn. 
The grits associated with the conglomerate are sometimes purplish 
where the conglomerate is purple, as near the Poorhouse on the 
Bangor road, but sometimes grey or yellowish, even when the con- 
glomerate is purple. Generally the grits underlying the conglo- 
merate are grey and yellow, as near Wern and Fachell. 
About a quarter of a mile N.K. of Fachell, in a large quarry by 
the road opposite Tymawr, the conglomerate is well seen. Its 
general colour is purple, and on closer examination it is seen to be 
composed of pebbles of great variety, from a grey or salmon-pink 
quartz felsite to a bright porphyry, in which red crystals of felspar 
shine in a black matrix. This conglomerate is followed by the 
usual Cambrian grits, sandstones, and mudstones, which are found 
a little further on much troubled by a great greenstone dyke. 
A fault which causes the smashed rock seen along the road by 
Fachell throws back the Cambrian to the W. of Llanddeiniolen. 
S. of this fault, near the church, black and grey banded flaggy 
shales occur, like those seen in a similar position E. of Bryniau 
