File:The Quarterly journal of the Geological Society of London (13204723273).jpg

NORTH-WEST OF ENGLAND AND NORTH WALES.
115
In the cuttings of the railway from Bettws up the Dolwydellan
valley, which I inspected in February 1876, while under construc-
tion, small patches of stratified gravel are here and there intersected ;
but, as a rule, very little drift was met with. About three quarters
of a mile from Bettws a cutting in the slate rock disclosed a
singularly smooth surface which had been protected by a cover of
drift ; it was not planed down, but was in undulating dimples and
hollows, smoothed as if ground with polishing paste. This was very
instructive, as where the rock was unprotected by drift on the same
shoulder, close by, without any transition, the rock was jagged and
irregular.
On a rock near to the mouth of the tunnel, but not on the line of
railway, towards the summit-level of the railway, some singular
markings were to be seen. They appeared as if gouged out at all
angles ; I have never seen any thing like this before or since.
Slate rock.
b. Drift.
In inspecting some excavations made for a sett quarry near the
Rivals mountain, I was struck with the jagged nature of the rock
underlying the drift .a, fig. 31), the very antithesis of that I have
described near Bettws. The drift b was compact and solid argilla-
ceous matter or Till, full of rough stones intermixed with angular
and subangular ones : some of the stones were erratics ; but most con-
sisted of the local felstone porphyry. I must bring this account of
the Welsh drift to a close by a description of the section disclosed by
the excavation of the puddle-wall of the Rhyl Reservoir* (fig. 32).
Fig. 32. Rhyl Reservoir, Nant Uwydd ; section of puddle trench.
(Horizontal and vertical scales 220 feet to 1 inch.)
JntendiS, water 7zne
Here we have : —
A. Bed rock, Denbigh Shales, getting more slaty in structure
towards y. The floor is quite level ; but the beds dip up the valley at
an angle of about 12°. The sides are stepped.
B. Fine waterworn gravel, angular and larger near the bed-rock.

• I ain indebted to Mr. H. C. Beloe, the engineer of the works, for this in
  

formation.