1 877-] The Great Ice Age and Origin of the <c Till .” 223 
What, then, must become of the chips and filings of these 
outfloating glaciers ? They must be carried along with the 
ice so long as that ice rests upon the land ; for this debris must 
consist partly of fragments imbedded in the ice, and partly 
of ground and re-ground excessively subdivided particles, 
forming a slimy mud that must either cake into what I ma}f 
call ice-mud, and become a part of the glacier, or flow as 
liquid mud or turbid water beneath it, as with ordinary 
glaciers. The quantity of water being relatively small under 
the supposed conditions, the greater part would be carried 
forward to the sea by the ice rather than by the water. 
As the glacier with its lower accumulation advanced into 
deeper and deeper water, its pressure upon its bed must 
progressively diminish until it reaches a line where it would 
just graze the bottom with a touch of feathery lightness. 
Somewhere before reaching this it would begin to deposit 
its burden on the sea-bottom, the commencement of this 
deposition being determined by the depth whereat the tenacity 
of the deposit, or its fridtion against the sea-bottom, or 
both combined, becomes sufficient to overpower the now- 
diminished pressure and forward thrusting, or erosive power 
of the glacier. 
Farther forward, in deeper water, where the ice becomes 
fairly raised above the original sea-bottom, a rapid thawing 
must occur by the adtion of the sea-water, and if any com- 
munication existed between fhis ice-covered sea and the 
waters of warmer latitudes a further thawing must result 
from the currents that would necessarily be formed by the 
interchange of water of varying specific gravities. Deposi- 
tion would thus take place in this deeper water, continually 
shallowing it or bringing up the sea-bottom nearer to the 
ice-bottom. 
This raising of the sea-bottom must occur not only here, 
but farther back, i.e., from the line at which any deposition 
commenced. This line or region, whereat the depth is just 
sufficient to allow the ice to rest lightly on its own deposit 
and slide over it without either sweeping it forward or depo- 
siting any more upon it, becomes an interesting critical 
region, subjedt to continuous forward extension during the 
lifetime of the glacier, as the deposition beyond it must 
continually raise the sea-bottom until it reaches this critical 
depth at which this deposition must cease. This would 
constitute what I may designate the normal depth of the 
glaciated sea, or the depth to which it would be continually 
tending, during a great glacial epoch, by the formation of a 
submarine bank or plain of glacier deposit, over which the 
