108 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ Dec. 8, 
which I have been deducing from physical evidence; for though 
we do not find any one of the peculiar shells of Bridlington amongst 
them, all of them belong to existing forms, and one, the uddeval- 
lensis variety of Mya truncata, is unknown either to the Crag, to 
the Lower, or to the Middle Glacial, and is also unknown at Brid- 
lington, while it occurs in the yet newer beds of the Clyde, and is 
still living. 
Very unlike the Bridlington fauna also is that of Moel Tryfaen, given 
in detail by Mr. Darbishire*. The list from that place is moreover 
equally unlike that of the shells from the Middle and Lower Glacial 
and from the Crag. The Moel-Tryfaen fauna, however, must have 
lived when this country was depressed nearly as much below the 
present sea-level as it was when the Shap boulders came over into 
the purple clay; but we must recollect that equal degrees of de- 
pression do not necessarily, even if the movement were uniform, 
imply an identity in age between deposits accumulated under them, 
since the one deposit may have been formed when the land was 
going down, and the other when it was rising, and the two be thus 
separated by a not inconsiderable interval of time, during which 
material changes in temperature may have occurred. ‘The Moel- 
Tryfaen bed therefore, instead of being synchronous with the pur- 
ple clay without chalk, may not improbably belong to the epoch 
of emergence—that is to say, to the very earliest part of the Post- 
glacial period, that, in fact, to which Mr, A. Geikie refers the stra- 
tified drift of Scotland. 
The prevalence of high land throughout Scotland, coupled with 
its higher latitude, concur to suggest that the ice-sheet would cling 
to that country after the far less elevated and more southern dis- 
tricts of the east and east centre of England had become freed from 
it; and the belief is therefore strong with me that the Glacial beds of 
Scotland belong, if not wholly, yet in greater part, to such later deposits 
as the north-of-England Glacial clay. One remarkable exception, 
however, exists to this, in the Aberdeenshire bed described by Mr. 
Jamieson in the 16th vol. of the Society’s Journal (p. 347), which, 
both in its physical structure and organic contents, seems to agree 
with the Middle Glacial formation of England. 
Note.—Since this paper was sent in with the lower representa- 
tion of the triple section drawn to such a supposed submergence 
(1500 feet) as would cover Stainmoor Pass with sea, I have been 
enabled, by-the kind assistance of Mr. Thos. M‘K. Hughes (who is 
engaged on the geological survey of the district), to pomt out what 
other routes than that of Stainmoor Pass exist by which floating 
ice bearing Shap boulders could, so far as elevation is concerned, 
have passed the dividing ridge under such a submergence as repre- 
sented. These routes are as follows :— 
1. Up the valley of the Eden, and so over into the valley of the Ure, and 
thence into Wensleydale. 
* Geol. Mag. vol. ii. p. 298. 
* 
