THE POLAR GLACIERS. 703 



of land, and in the southern, so far as is known, about 16,000,000 square 

 miles. Now, the great problem in physical geography is. What is 

 there in the southern hemisphere to counterbalance this great excess 

 of land in the northern ? 



Humboldt has estimated that, if the mountains and highlands of 

 Asia were leveled down and made to fill up evenly the low places, the 

 whole continent would have a uniform height of 1,150 feet above the 

 sea. In like manner. South America would have a height of 1,130 

 feet ; North America of 750 feet ; and Europe of 6*70 feet. The aver- 

 age of the whole he estimates at 920 feet. Of the mainlands not 

 included in the above namely, Africa, Australia, the polar lands, and 

 islands about as much is north as south of the equator. So that we 

 may safely estimate that there is in the northern hemisphere an excess 

 of 28,000,000 square miles of land, of the average height above-men- 

 tioned, to be counterpoised by something yet to be found in the south- 

 ern hemisphere. 



If there is an excess in the quantity or bulk of water south of the 

 equator over that north of it, then the difference of weight between 

 this excess and so much land, which is about in the proportion of one 

 to two and a half, must be added to the unknown quantity which we 

 are soon to look for above the southern seas. As there is, of course, 

 the same excess of water-surface south of the equator that there is of 

 land-surface north of it, and as we may very safely assume that the 

 oceans have a mean depth of at least 3,220 feet (3|^ X 920) and that the 

 southern waters average as deep as the northern, it follows that our 

 unknown quantity is at the very least doubled by the above consid- 

 erations. We have, therefore, to seek in the southern hemisphere 

 what will balance 28,000,000 square miles of land at least 1,840 feet 

 high. 



We look over the map of the world, and down near the bottom we 

 find some uncertain landmarks with many breaks, but on the whole 

 tracing out very nearly the antarctic circle, and indicating that there 

 is, covering nearly all that zone, an unexplored and scarcely discov- 

 ered country. This impenetrable region is estimated to be as large 

 as the continent of North America, about 8,000,000 square miles. 

 A very little arithmetic will now prove the bold claim which I here 

 make, that, even supposing the whole of this region to be land of the 

 average continental height, there is still required over it all an average 

 thickness of two and a half miles of solid ice to make the southern 

 hemisphere equal the northern in weight. 



This result of calculation is well confirmed by the information 

 which all southern navigators have brought back from those most 

 desolate and ice-bound regions. The zone of the antarctic has been 

 encroached upon only in a small space south of the Pacific. On every 

 other side, so far as has been discovered, mountains of ice block the 

 way on and near the polar circle, which seems to be the great ice-bar- 



