Vol. 58. ] GLACIER-LAKES IN THE CLEVELAND HILLS. 563 
that at two places, Whitby and Robin Hood’s Bay, it has been 
found in situ in Lower Boulder-Clay, no further argument seems to 
be needed to prove that the earliest stage of glaciation was effected 
by the Shap- Granite-bearing Teesdale stream. This conclusion is 
a reversion to an early opinion of mine, which was (I am bound to 
say) scarcely warranted by the information that I then possessed. 
The many and far-reaching assumptions which such a conclusion 
as this implies, are not realized until we have considered what must 
have been the condition of the Irish-Sea drainage-basin at the 
time when a regurgitation of the ice flowing down the Vale of 
Eden was produced, and the lofty ridges near the headwaters of 
the Tees were overridden by the reversed flow. The Irish Sea 
was the common receptacle for ice, not only from the mountains 
of Wales, the Lake District, the South-west of Scotland and of 
Ireland, but the extreme state of congestion to which the Stain- 
moor overflow was due may be said to have resulted from a great 
influx of ice from the Clyde. Clear testimony to the fact of this 
influx is furnished by three lines of evidence. The strie upon rock- 
surfaces in Ayrshire and on the Mull of Galloway show a gradual 
sweep-round of the ice, so that both the Mull of Galloway itself and 
the low grounds south and east of Loch Ryan were overridden. 
Fragmentary shells are found in the Drift about Loch Ryan, 
which is what might be expected if the ice out of the Clyde had 
moved over the land; and, finally, the copious dispersal of the very 
characteristic Clyde rock, the eurite of Ailsa Craig, over the Irish 
Sea, and especially in the Isle of Man and the North-east of Ireland, 
proves that the movement was upon a large scale. 
Tracing our chain of causation backward link by link, we may, 
I think, enquire what caused the Clyde ice to attain such propor- 
tions; and we find here a clue in the signs which exist down the 
whole of the eastern coast-line of the British Isles, from the Orkneys 
to Norfolk, of the pressure of a great ice-sheet, the radiant point of 
which was somewhere in the neighbourhood of the head of the Baltic. 
The evidences of this pressure are too well known to need any 
description here, but among its effects were not only a deflection of 
our eastward-flowing ice into a northerly or southerly coastwise- 
flow, but a general shifting of the Scottish line of ice-shedding 
towards the eastward, so that erratics from the Eastern Highlands 
were carried over the watershed and out to the west coast. 
This effect was felt at the mouth of the Firth of Forth, and 
though I canuot ascertain that any erratics have crossed the water- 
shed into the Clyde, yet I do not think it can be doubted that, but 
for the obstruction of the ice-sheet in the North Sea, a much larger 
proportion of the Highland ice descending into the great Lowland 
Valley of Scotland would have gone into the North Sea. 
If this be granted, then it follows that the Scandinavian ice- 
sheet was the direct cause of the excess of ice in the Clyde, which 
by overflowing into the Irish Sea caused the reversal of the ice-flow 
in the Vale of Eden, and the consequential descent of the Teesdale 
Glacier to the sea at Teesmouth. It may be objected that the 
