234 LAMPLUGH : SHELLY MORAINE OF THE SEFSTROM GLACIER. 
It is evident that many of the shells now on Cora Island are 
the rehcs of molluscs that were actuaUy alive just before the 
advancing glacier swept them from their habitat in the fiord, along 
with the clay deposited there. The presence of the species not 
now extant indicates, however, that the glacier did not merely 
scrape the surface of the sea-floor, but ploughed down into it ; 
for the muddy waters of the bay must constantly precipitate 
much sediment, so that the ancient sheUs were probably buried 
at some depth. The abundance of Mytilus edulis in the moraine 
shows that, whatever may have been the thickness of the over- 
l3ring sediment, the ice-plough went, at any rate, deep enough to 
reach and transport the layers representing the by-gone period 
of milder conditions. 
It is hardl}^ possible to fix the exact distance that the shells 
have been carried, as we do not know at Avhat stage of its ad- 
vance the glacier began its dredging. Presumably the effect 
was greatest when the ice impinged on the rising slope of the sea- 
bottom near the island, in which case the distance would not be 
over a mile ; but if the operation began earlier, the shells may have 
been carried for three or four miles. The vertical uplift from the 
deepest part of the fiord to the highest part of the moraine may 
have been about 250 feet ; in most cases it has probably been 
somewhere between 50 and 100 feet. Even with so short a 
journey, the marine material showed hardly any trace of its 
original order, except in some patches, seen by Dr. Strahan, 
in the portion stiU entangled with the ice. If the glacier had 
continued to move forward, the material must have been carried 
farther ; in fact there is every probability that some part of it 
would have been carried along to the farthest limits attained 
by the ice, and would there have been cast down pell-mell, as 
soon as the retreat set in. During a longer journej^, however, 
the shells could hardly have retained their perfect condition ; 
they would have ' gone farther and fared worse," becoming 
gradually reduced to the fragmentarj' and travel-worn state Jof 
the specimens mth which we are so familiar in our British shelly 
drifts ; but in the patches of ' Bridlington Crag " of the Basement 
Boulder Clay of Bridlington, South Sea Landing, and Dimlington, 
the shells are in the same condition as those of the Sefstrom 
moraine. 
