28 NOTES ON THE GEOLOGY OF 
Everything fits in with the hypothesis that the mixed 
Clwydian Drift belongs to a period when the glacier ice had 
receded, and the sea was working away at sorting and trans- 
porting the ancient glacial drift and mixing it up with the 
shingle travelling along the shore, and perhaps some débris 
borne by shore ice from the north and east. 
What was the extent of the submergence which followed the 
Glacial Period? If I am right in referring the gravelly drift 
about Bryn-y-pin and the granite boulders along the top of the 
ridge south of Fronhaul to this period, then the sea must have 
rolled over the bounding hills on both sides of the valley. 
How much deeper they went we cannot say, but this is not 
nearly so great as the known submergence of 1,350 feet on 
Moel Tryfaen, or even of 1,250 at Macclesfield. 
I will now call attention to some other sections in which the 
details of these drifts may be studied. 
It is well developed at the west end of the estuary about 
Colwyn (see fig. 13.) 
Fic. 13. 
Section tn promontory, about 200 yards N.W. of Bath House, 
Aberrhyd, Colwyn Bay. (Scale, 20 feet to 1 inch.) 
a. Chocolate-red clay, with scratched stones. 
6. Sand. i 
c. Yellow laminated sandy clay. 
d. Blue clay with scratched stones. 
In the Limestone Quarry near last “‘r” in Parc-y-milwr, near 
Abergele, there is a great mass of sand and gravel which I 
would refer to the Clwydian marine drift. It consists of 
angular, sub-angular, and rolled fragments of carboniferous 
and grey rocks, and abuts against an irregular cliff of Mountain 
Limestone. 
In the valleys of the Elwy and the Clwyd, we find the same 
drift exposed in many natural and artificial sections (see fig. 14.) 
FIG. 14. 
Section seen in cast bank of Elwy below The Mount, St. Asaph. 
(Scale 40 feet to 1 inch.) 
a. Marine drift with shells—see Zist. 
Consists of alternations of brown or red clay and loam with beds of 
sand and gravel. Varies much from year to year as the river cuts 
back the cliff. Generally the middle part is distinctly banded 
with alternate more sandy and more loamy beds. Scratched 
stones not common. Flint and granite as well as boulders from 
Welsh hills. 
é. Blue clay with many scratched stones. Boulders all from Welsh 
hills except in top part. 
A similar section is seen in the river cliff S. of Brynelwy, near 
St. Asaph. 
