THE GLACIAL DEPOSITS OF NORTHERN PEMBROKESHIRE. 85 
ness, even if we allow that the land at that time stood at a somewhat lower level 
than it does at the present day. Mr LampiucH gives a sketch-map of the Irish 
Sea (as far south as the Lleyn promontory), showing glacial strize and probable direction 
of the ice-movement. The ice which streamed over the Isle of Man from the north 
_is shown as usual to have travelled south and to have overwhelmed Anglesea, being 
here diverted so as to move more to the south-west on account of the opposition of 
the ice coming down to meet it from the mountains of Snowdonia. On the western 
side of the Irish Sea basin the strize indicate that the ice moved from the land on 
the eastern seaboard of Ireland, and took a course from north-north-west to south- 
south-east, and coalesced with that which passed over Anglesea and Lleyn. Its course 
southwards from this limit is not shown. But in Professor Grrkin’s map the Irish 
ice is made to bend back to the south as a result of its meeting with that part 
of the ice-sheet which flowed over Anglesea, and the northern ice is shown as passing 
down to the west of Cardigan Bay, on account of the presence of the ice flowing west 
from Merionethshire and Central Wales. But the investigations carried out on the 
glaciation of Pembrokeshire make it clear that the Irish ice was not bent back so 
sharply, but, on the contrary, it continued in its original course from north-north-west 
to south-south-east, whilst the ice from the north was forced to invade Cardigan Bay, 
and must therefore have shouldered in the Welsh ice again upon the mainland. This is 
proved by the direction of the striz seen along the coast, as well as by the presence 
of boulders of igneous rock from Ireland and the south of Scotland in the drift as 
far east as Cardigan. Again the presence of chalk-flint throughout the area is evidence 
in the same direction, for these must have come from the north-east of Ireland or 
from the bed of the Irish Sea; and it is possibly from this bed that the boulders of 
Carboniferous Limestone which are seen so abundantly at Cardigan have come. 
In this connection it is interesting to recall the presence of fragments of Millstone 
Grit in the gravels at Pen Creigiau. Our knowledge of the glaciation of Ireland is 
as yet very imperfect, and it is difficult to estimate what volume of ice passed seawards 
from its eastern border. At the present day the rainfall over Ireland is very excessive, 
and so it seems probable that the snowfall was likewise excessive during glacial times. 
This would give rise to a proportionately large ice-sheet moving outwards in all 
directions, and so it is quite possible that the amount of ice which found its way into 
the Irish Sea basin was considerably greater than has been generally supposed. And 
in the southern part of the basin it would to some extent oppose the passage of the 
western ice which overflowed Anglesea and the end of Lleyn in a south-westerly 
direction, and cause it to turn a little more to the south so as to travel over Cardigan 
Bay. The confluent sheet, forming by the junction of the Northern ice, the Irish 
ice, and to some extent the Welsh ice, would invade northern Pembrokeshire in the 
direction which is shown by the striz along the coast near St David’s, namely, from 
north-west to south-east, or perhaps from north-north-west to south-south-east. This 
would explain the transport of boulders from the St David’s Head gabbro south- 
TRANS. ROY. SOC. EDIN., VOL. XLI. PART I. (NO. 4). 14 
