Thickness of the Antarctic Ice , anf its [January, 
16 
Examination of the Reasons for supposing that the 
Antarctic Ice-cap is not of Enormous Thickness. 
i. Limit to the Thickness of the Ice resulting from Melting 
produced by Pressure . — Pressure will produce a melting of 
the ice in two totally different ways, viz., either by lowering 
the melting-point or by the work of compression. I shall 
consider both cases, and see if any ground is afforded by 
either in support of the conclusion that the Antarctic ice 
can be only one or two thousand feet in thickness. 
{a.) Melting produced by the Lowering of the Melting-point.— 
The pressure exerted by a column of ice of half a mile in 
height would, as we have seen, lower the melting-point i° ; 
consequently, if the column were at the temperature of 32 0 , 
its base, being i° above the melting-point, would not remain 
in the solid condition. To prevent the ice melting, the tem- 
perature of the base would require to be as low as 31 0 . 
Therefore, if 32 0 were the temperature of the Antarctic ice, 
Sir Wyville Thomson’s conclusion, that the sheet cannot 
be more than 1400 feet in thickness, would follow as a 
matter of course. 
But his supposition that, owing to internal heat coming 
through the earth’s crust, the bottom of the Antarctic ice- 
sheet is kept at the temperature of 32 0 , cannot be sustained. 
It is this fundamental error, as I conceive it to be, which 
has led Sir Wyville astray, and induced him to believe that 
the ice cannot be of excessive thickness. 
“ The normal temperature of the crust of the earth,” 
says Sir Wyville, “at any point when it is uninfluenced by 
cyclical changes, is, at all events, above the freezing-point, 
so that the temperature of the floor of the ice-sheet would 
certainly have no tendency to fall below that of the stream 
which was passing over it. . . . In fadt, ice at the temper- 
ature at which it is in contact with the surface of the earth’s 
crust within the Antarctic regions, cannot support a column 
of itself more than 1400 feet without melting.” 
In the question under consideration we are diredtly con- 
cerned with the temperature of the surface of the earth’s 
crust only, — the floor on which the ice-sheet rests, — and not 
with the temperature below the surface. It is pefedtly true 
that at considerable depths below the surface internal heat 
maintains a temperature above the freezing-point ; but it is 
not true that it does so in reference to the surface. Under- 
