1822.] Geology of Snowdon, and the surrounding Country. 408 
feet from the road to view one of the finest waterfalls of North 
Wales, Rhiadr Mawr, which is about six miles on the south of 
the latter place. It descends from the mountain region through 
a narrow chasm where the rocks are laid bare. The same rocks 
and slates were visible here also, the prevalent rock being that 
which has the most homogeneous and compact aspect, and 
which likewise is the prevailing rock of Moel Shabod. In some 
instances, it contained harder masses imbedded in it of the same 
composition as the rock itself, which here also contains calca- 
reous spar and opaque felspar(?). Slates predominate just above 
the paper mill, situated about 100 feet above the road. From 
this place to Conway, the slates continue ; they are often in a 
very decayed state, and the road, where it is repaired with them, 
is in many places as black as if the shale of a coal-field had 
been employed. The direction of the cleavage is as before 
noticed. 
A letter from the Rev. W. D. Conybeare having mentioned 
the existence of a felspathic rock in the hill above Conway, 
with a request that it might be attentively examined, we became 
desirous of giving our best attention to its discovery, and were 
prepared to expect in the nature of the rocks we were about to 
observe, a great difference to those we had so lately been attend- 
ing to. 
‘his hill rises gradually at a little distance on the west of 
Conway, extending about three miles towards Bangor, its north- 
ern limit being the sea. We walked the greater part of the way 
along the summit ridge, descending to the high road, perhaps 
one-quarter of a mile before its termination, which is too rough 
and abrupt to admit of descent. In this walk, we did not per- 
ceive any well characterised slates; the rocks, however, espe- 
cially at the termination of the hill near Conway, have a deci- 
dedly slaty structure, particularly apparent on the surface, with 
the plane of cleavage distinctly ranging E and W; that is to 
say, nearly at right angles to that in which it had uniformly 
* ay heretofore ; the dip is towards the south at a high 
angle. 
it is often only by a very attentive comparison of a suite of 
rocks which in themselves are but varieties of the same compo- 
sition, that we can perceive the alliance of the two extremes, 
which not uncommonly are so dissimilar as to appear perfectly 
distinct in their nature and composition. So is it with the rocks 
of the hill in question. 
The first rock which presented itself immediately on ascend- 
ing the hill, bears a general resemblance to the prevailing rock 
of the base of Moel Shabod in texture and aspect; it is, how- 
ever, somewhat harder, and would appear perfectly homogene- 
ous, but for the existence of a few minute specks of crystal- 
line quartz, and also of a substance of a dark-green colour, which 
202 
