92 LIVERPOOL BIOLOGICAL SOCIETY. 
The view that these deposits were formed by icebergs 
stranding on the hill, is open to serious objections, since 
the bed is on the lee side where such stranding could not 
occur, and the terminal curvature of the slates on which 
the sands rest curve down the hill, as Professor Bonney 
pointed out, and thus could not have been so caused. The 
beds, moreover, are much contorted, in a manner very 
suggestive of the action of land ice. The strongest 
objection, however, is that a submergence to this depth 
would have left far more conspicuous traces than actually 
occur, as it could not have failed to have swept away many 
of the light drift beds of the district, and would have left 
more marine beds in the hollows of the Welsh hills, in 
which such would have been so readily deposited, and so 
admirably sheltered and preserved. | 
Having thus seen that the marine origin of the Moel 
Tryfaen drifts is improbable, alike from the distribution of 
the beds, their lithological characters, and their fossil 
contents, it remains to consider the alternative theory of 
their deposition. It is one of the best known facts of 
glacial motion, that the lowest layers have a constant 
tendency to work their way up to the surface, carrying 
with them any boulders they may contain. Whatever 
theory we may adopt to explain this, the fact remains that 
under the combined influence of ablation and turgesence 
the boulders will rise to the surface; hence as the ice 
sheet flowed over the Irish Sea, it picked up flints, shells, 
&c., which would probably freeze together into boulders, 
and so work their way up through the ice to a level from 
which, on the melting of the ice sheet, they would be 
deposited on the neighbouring hills. 
It must of course not be forgotten that though these 
views are steadily gaining ground, the balance of opinion 
at present favours the older theory, and therefore these 
