30 ' Thickness of the Antarctic Ice , and its [January, 
At the close of the reading of Dr. James Geikie’s paper 
“ On the Glacial Phenomena of the Long Island,” before the 
Geological Society, in May last, His Grace the Duke of Argyll 
stated that he doubted whether ice could move on a slope of 
i in 211. But a slope so small as i in 211 would give a 
thickness of 7 miles at the Pole. Consequently we have no 
alternative but to admit that a slope of 1 in 211 is sufficient, 
or the cap must be over 7 miles thick at the Pole.* 
But to avoid all objections on the score of over-estimating 
the thickness of the cap, let us assume that a slope of an 
eighth of a degree would be sufficient to produce the neces- 
sary motion ; the thickness of the sheet would of course be 
one-fourth that represented in the diagram, but still it would 
be 3 miles thick at the Pole ! 
There is another cause which tends to mislead us in 
forming an estimate of the aClual thickness of the Antarctic 
ice. It is not in consequence of any a priori reason that can 
be urged against the probability of such a thickness of ice, 
but rather because it so far transcends our previous expe- 
rience that we are so reluCtant to admit such an estimate. 
If we never had any experience of ice thicker than what is 
found in England, we should feel startled on learning for the 
first time that in the valleys of Switzerland the ice lay from 
200 to 300 feet in depth. Again, if we had never heard of 
glaciers thicker than those of Switzerland, we could hardly 
credit the statement that in Greenland they are actually from 
2000 to 3000 feet thick. We, in this country, have long 
been familiar with Greenland; but till very lately no one 
ever entertained the idea that that continent was buried 
under one continuous mass of ice, with scarcely a mountain 
top rising above the icy mantle. And had it not been that 
the geological phenomena of the Glacial epoch have for so 
many years accustomed our minds to such an extraordinary 
* Dr. J. Geikie writes me as follows : — “ I have given the height of the 
glaciation in the North-west Highlands as 3000 feet or thereabout, which, 
taken in connection with the glacial phenomena of the Outer Hebrides, 
implies a slope for the surface of the ice-sheet of 1 in 211, or about 25 feet in 
the mile. It is not impiobable, however, that a more detailed examination of 
the mainlands may compel up to admit a still greater thickness for the ice- 
sheet of the North-west — the surface of which may have reached to a height 
of 3500 feet in Rosshire. This would yield a slopeof 35 instead of 25 feet in the 
mile. After my paper had gone to press I received, through the kindness of 
Mr. George H. Cook, State Geologist of New Jersey, a copy of his Annual 
Report for 1877, in which the slope of the ice-sheet that flowed into the 
northern part ot that State is estimated at 34 feet in the mile. Prof. Dana, 
you will remember, comes to the conclusion that the surface of the ice-sheet 
attained a height upon the Canadian water-shed of 12.000 feet, on the 
supposition that the ice sloped southwards at the rate of 10 feet in the mile, — 
it the slope were greater, the Canadian ice, of course, must have been 
thicker. The inclination of the ice-sheet in the area of the North Sea I esti- 
mate at about 12 or 13 feet in the mile/’ 
