TRANSACTIONS OF SECTION C. 801 
4. The Glacial Phenomena of the Vale of Clwyd. 
By J. Lomas A.R.C.8., and P. F. Kennan, £.G.8. 
The Vale of Clwyd is a V-shaped valley running almost N. and 8S. The floor 
is composed of Triassic rocks, while the sides consist of Silurian slates and grits 
with faulted inliers of Carboniferous age at intervals along the inner edges. 
The tract of land occupying the mouth of the Vale is low and marshy. As 
the solid rock is reached in this district only at a considerable depth below O. D., 
and there are evidences of a pre-Glacial line of cliffs along the neighbouring coasts, 
we must regard it as an arm of the sea which has been filled up with drift 
deposits. 
. About St. Asaph and southwards the ground rises into mounds which run 
nearly parallel to the axis of the Vale. Where gaps appear in the Moel Fammau 
range the drift mounds curve round so as to be parallel with the opening. 
Further south, beyond Denbigh, the ground is again flat, and this character con- 
tinues to the end of the open part of the Vale. 
“The deposits at the north consist of clays and sands with shell fragments 
similar to those spread over the plains of Lancashire and Cheshire, and contain 
erratics from the N. 
* At St. Asaph, Colwyn, and other :places these northern drifts are seen to 
overlie an older deposit -yielding Welsh erratics exclusively, and containing no 
shell fragments. 
The northern drift extends as far as Tremeirchion on the east, and a boulder of 
Scotch granite has been found near Denbigh on the west. 
Above Denbigh only Welsh drift is found. 
Near Llanfair the Clwyd leaves the main valley and goes through a gorge con- 
tinuing tonear Corwen. At Pwll-glas, Derwen, Gwyddelwern, and other places the 
valley is blocked by mounds of gravel which run athwart the valley. They repre- 
sent terminal moraines laid down by a glacier proceeding down the Vale from the 
Dee Valley. 
Sequence of Events.—The Welsh hills nursed glaciers during the early part of 
the Glacial period. These increased and spread out from Arenig Mawr asa centre. 
So great was the ice-spread that boulders were carried over the highest points in 
the Moel Fammau and the Mynydd Hiraethog and Cyrn-y-Brain ranges. 
The ice from Scotland, Lake District, and Ireland, creeping southwards and 
filling the shallow Ivish Sea, cleaved on reaching the N. Wales massif about the 
Gt. Orme’s Head. 
So great was the pressure that the Welsh ice was also divided into two streams, 
one going west through the Menai Straits and over Anglesey, and the other going 
eastwards and joining with the great sheet which swept over Cheshire into the 
Midlands, 
Evidence of this cleavage we have in the Glacial strie which are divergent E. 
and W, of the Conway and in the character of the boulder transport. The E. side 
of the Vale of Clwyd is covered with great deposits of red drift derived from the 
floor of the Vale, while the W. side contains no Triassic rocks. Through the 
opening about Bodfari enormous masses of red sand were carried, and formed the 
well-known deposits of the Wheeler Valley. 
On the dwindling of the ice the valleys still retained small glaciers, the 
deposits of one being found in the Upper Clwyd. 
Conclusions. —The Drift lends no countenance to the theory that this portion 
of North Wales was submerged during the Glacial period. In fact the absence of 
northern Drift with shells in places at a level below the shell-bearing beds on each 
_ side directly contradicts the assumption. 
| 5. On some Post-Pliocene Changes of Physical Geography in Yorkshire. 
By Percy F, Kenpat, £.G.S. 
The drift deposits of Yorkshire are extensively developed over all the low 
grounds and in much of the hill country. They have been attributed by the 
