At the poles the surface is thus thirteen miles nearer to these tremendous fires.

Of course it may be supposed that the earth's crust is of about equal thickness on all parts; yet still, even if this be so, thirteen miles ought to make some difference.

Now at the North Pole there seem to be causes at work to counterbalance the effect of the internal heat, chiefly in the enormous accumulation of polar ice which probably hems it in on every side; and though many believe in an open polar sea of warm water at the North Pole, yet still the effect of vast ice-masses and of cold submarine currents must be to render the climate severe.

But at the South Pole it is different.

The observations of Ross and of More show us that there is a chain of mountains of immense height, which seem to encircle the pole.