James Durham—Pleistocene Geology, Firth of Tay. 545 
The argument is brought nearer home to us when the submergence 
toa great depth of a large part of the British Islands during the 
“ Great Ice Age,” is put forward as evidence that the weight of ice 
and snow is sufficient to press the land so encumbered down into 
the sea. It is this last part of the argument that I propose to 
briefly examine. 
Now there is no doubt whatever that during the Glacial period 
very considerable subsidences of the land took place, which looked 
at in a broad and superficial way seem to support the new theory ; 
but a closer examination of the details of these depressions and 
subsequent elevations fails to show that they give that satisfactory 
support to these speculations which is expected of them. 
The estuary of the 'l'ay and its neighbourhood perhaps affords as 
good examples of the traces of these changes of level as are to be 
met with within such a limited area, while the hills that approach 
its margin or can be seen from it, bear very aprilcing testimony to 
the enormous effects of glaciation. 
In looking at the valley of the Tay, one immediately recognizes 
as perhaps the most interesting feature of the landscape, the smoothed 
and rounded appearance of the hills, on all hands soft and waving 
outlines, just relieved here and there by comparatively insignificant 
escarpments, the result of subaerial denudation, the cutting of 
streams, or the battering of the sea. The hard and intractable 
gneisses of the far-off Highland mountains, the hard sandstones 
and associated volcanic rocks of the nearer hills, are all reduced to 
one uniform smooth contour, pointing out unmistakably that through- 
out the whole, or almost the whole, Glacial period these rocks must 
have been subjected to the grinding action of the ice-sheet, which 
could only have been the case if the land stood at least as high as at 
present during its continuance. As has been shown by the presence 
of certain strata of sand and shells intercalated between beds of 
Till, a depression of the land to a depth of at least 500 feet took 
place i in the comparatively early part of the “Ice Age,” but the fact 
that these stratified beds exist upon the ground moraine of the ice- 
sheet seems to show conclusively that at the time of their deposition, 
the ice was very greatly reduced, had retired from the coast-line, 
and possibly disappeared altogether. It is further evident that the 
duration of this great submergence was relatively short, for while 
the ice has left such tremendous record of its presence all over the 
land, the encroachment of the sea, as far as I can find, has left no 
other evidence than the beds of sand, etc., referred to. 
Traces of the last great advance of the ice-sheet and the changes 
that afterwards took place are necessarily much more distinct than 
that of the first and greatest extension of the ice, and they na 
remarkable manner repeat the same line of evidence as the first. 
Rocks sheltered from the action of the waves frequently bear well- 
marked glacial striz, and these can be seen to pass under the level of 
the sea, showing that at the last glaciation of the land it stood higher, 
than at present. The thickness of the ice must have been very 
considerable as it flowed over Dundee Law, a conical hill upwards. 
DECADE II.— VOL. X.—NO. XII. 39 
