Prof. Edw. Hull—Submergence of the British Isles. 105 
Treland. Prof. Lewis, however, struck out a new theory to account 
for the existence of these high-level shelly-gravels, which has since 
been adopted by Mr. Kendall' and other geologists, according to 
which these shell-beds have reached their present altitude by the 
agency of the great ice-sheet, which is credited with the astonishing 
power of having carried these deposits from the bed of the Irish 
Sea, and then of having laid them down in their final resting- 
place high up amongst the mountain groups of Wicklow, Wales, and 
Central England. It might be objected to this view, that, in the 
first place, the matter deposited at the tail of an ice-sheet is moraine 
matter, not usually stratified shelly gravel and clay; in the second, 
that in the process of transportation, such deposits, borne along for 
miles in the body, or at the foot, of the ice-sheet, and carried up the 
mountain slopes, would be ground into the finest mud or powder; 
and it seems inconceivable that even a few minute fragments of 
shells, sufficiently large for identification, should have survived such 
a destructive process; but this objection is considered invalid, so 
that we must have recourse to others. 
Well then, thirdly, the view advocated supposes either that the 
ice-sheet in the Irish Sea attained an original thickness of 1300 
or 1400 feet in the vicinity of the mountains aforesaid plus an 
additional thickness for the depth of the adjoining sea-bed, or else 
that it rose up from the sea-bottom and ascended the flanks and 
valleys of the mountains owing to the vis a tergo, or some other 
force of propulsion. The thickness of the ice-sheet in the latitude 
of Snowdon must have been over 1500 feet according to this calcu- 
lation (a very improbable view as it seems to me); or the ice must 
have pushed the shell-beds several hundred feet up the Welsh and 
Wicklow slopes; a phenomenon which, as far as I am aware, has 
no example at the present day. In making this statement, I do not 
deny the power of glacier-ice to move over low opposing ridges, as 
in the case of Bray Head, but in such cases the whole of the opposing 
ridge has been enveloped in the mass of moving ice; and the 
conditions are very different from those which would occur where 
the ice-sheet is confronted by the flanks of still higher ridges. 
But without insisting too strongly upon this objection I have 
another to advance which is absolutely fatal to the transportation 
theory of Prof. Carvill Lewis and his followers. In the case of 
North Wales, those who are acquainted with its glacial phenomena, 
or who have studied the writings of the late Sir A. C. Ramsay, 
are aware that there is no evidence whatever of an ice-movement 
inwards from the Irish Sea; but that, on the contrary, the ice- 
movements radiated outwards from the mountain heights. Ramsay, 
indeed, clearly describes what he calls “the Drift,” and shows that it 
consists of Boulder-clay, sand, and gravel filling the bottoms and 
sides of the valleys up to a level of about 1300—1400 feet ; but 
that this Drift is of marine origin, formed during a period of sub- 
mergence, he has no doubt whatever. When describing it as rudely 
stratified, and containing blocks and boulders carried by floating 
1 Glacial Geology, Old and New. Grou. Maa. Dec. III. Vol. IX. p. 491. 
