1822.] Geology of Snowdon, and the surrounding Country. 419 
Carnarvonshire ; as, for instance, the greater part of the route 
by the old road from Pont Aberglasslyn to within a mile or two 
of Tan y Bwlch, which chiefly traverses the solid rock. 
The slates between the Mynfedd Inn and Machynlleth have 
the same dip and direction as those on the escarpment of Cader 
Idris. The houses of Machynlleth are all of slate. 
The country between Machynlleth and Aberystwith partakes 
of the same general character. Lofty hills, with steep and rapid 
slopes, and bounded by narrow vallies, frequently pretty well 
cultivated, the herbage covering even the summits of the hills, 
which are rounder than before. Woods of small oak, but of 
considerable extent, were frequent on the sides even when very 
steep. The rock rarely appears through the verdure, so that 
almost the only chance of gaining information respecting its 
nature is to be found in the little quarries beside the road, or 
where, as is sometimes the case, the unbroken rock constitutes 
the road itself. Many instances of this occurred soon after 
leaving Machynlleth, affording the opportunity of ascertaining 
that the direction of the cleavage, and the dip, still continue the 
same. The rock, however, is not always a pure slate, since it 
is very commonly interstratified, as every where eise, parallel to 
the direction of its cleavage, with thin layers of a granular stone, 
in its external character greatly resembling some of the varie- 
ties every where observable in the more northern mountains, but 
of a colour more nearly approaching that of the slate, and often 
consisting of variously coloured particles lying parallel to the 
plane of interstratification. 
We regret omitting the opportunity of examining the slate 
quarries of Aberystwith. We walked, however, to the bold 
projecting rocks at the point on the NW of the town, where 
we found almost the only instance of irregularity in the dip, and 
contortion of the strata, that we have observed. At the point, 
and as far as we could see the coast beyond it on the north, the 
dip appears to be nearly E at a low angle, although that of the 
rocks at its foot, which are covered at high water, dip in another 
direction ; and during the very short time we looked at these 
rocks, it appeared to us that those immediately in contact with 
the point, towards the town, and which are contorted, dip ina 
third direction ; but it is not improbable that further investiga- 
tion might have proved the inaccuracy of some of these appear- 
ances. Every where the slate is interstratified parallel to its 
cleavage plane with a more or less granular rock, much resem- 
am some of the finer-grained varieties of the base of Moel 
od. 
The same kind of country continued to the Devil’s Bridge, 
and very slight opportunities of examining the rocks on one side 
only of the road, afforded us only the information that the sum- 
tits of the hills are of slate, often in very small rhombic pieces, 
asthough, from some cause or other, they had been shattered. 
242 
