ROCKS OF CAERNARVON. 691 
Bangor; and W. of these, grits and purplish sandy shales crop out 
in the road and quarry near the Rectory. These are probably all 
above the conglomerate. 
Coarse grits, like those near Fachell, occur along the 8.E. flank 
of the hill for about three quarters of a mile near Careg goch, and are 
quarried here and there. They dip at about 30° to 40° 8.8.K. and 
E.S.E. I take these to be the base of the Cambrian, here irre- 
gularly and unconformably lying upon the felsites, and thrown back 
from the grits of Fachell by the same fault which repeats the Brithdir 
beds at Pantyfallen and Tanyperthi. 
Two miles further to the S.W. we find the grits and conglomerates 
flanking the Caernarvon beds on the $.H. sides of the ridge. They 
are first exposed in a small disused quarry, in a field on the top of 
the hill between Yscuborwen and Tygwyn, where they are seen 
dipping 45° to 48° 8.8.E. and§. 30° E. (fig. 10). The conglomerate 
Fig. 10.—Section in Quarry on top of hill between Vscuborwen and 
Tygwyn, Caernarvon. 
N.W. 8.E. 
a”, Tough sandstone and grit. 
a. Grit and conglomerate, with quartz, quartzite, lydian stone, Jasper, mica- 
schist, &c. 
consists chiefly of white quartz, among which pebbles of blood-red 
jasper are conspicuous, and less commonly fragments of mica-schists 
three or four inches in longer diameter. The conglomerates pass 
under tough grey grits and sandstone, which crop out under the 
hedge all along the opposite side of the quarry, as shown in fig. 10, 
which is drawn not quite at right angles to the strike, and therefore 
shows a somewhat lower angle than true dip. 
Less than half a mile S.W. of this a quarry is being worked close 
to the road recently constructed towards the top of the hill, near some 
new villas. In this a somewhat similar but finer conglomerate is 
seen faulted against the Twt-Hill rock, and passing with a dip of 
about 15° under very tough grey grit weathering yellowish (figs. 3 
and 4), The dyke fault, with a downthrow on the N.E., now 
throws the grits und conglomerates forward to the S.; and they are 
next seen in the quarry illustrated by fig. 2, resting on the Twt- 
Hill rock at an angle of about 65°, and dipping under grits and 
somewhat flaggy sandstones seen in the 8. corner of the quarry. 
The conglomerate has been cut back to the Twt-Hill rock, leaving 
patches adhering in places, owing partly to the irregularity of the 
base, and giving the appearance of alternations of Twt-Hill rock 
and conglomerate, dipping a little to the EK. or W. of 8. The true 
