THE POLAR GLACIERS. 707 



our winters are short and mild, and our summers long and sunny. 

 During the cycle which shall comprise the latter case, our winters will 

 be rio-orous and our summers short. The northern hemisphere is now 

 having its great summer. In about 10,000 years it will be in the 

 midst of its great winter; and whatever dilFerences there may be be- 

 tween the two hemispheres, owing to astronomical causes, will then be 

 in full force against the northern, 



A distinguished Scotch mathematician, Mr. James Croll,* has 

 estimated that the melting of a mile in thickness of the present ant- 

 arctic ice would raise the sea-level at the north pole 300 feet, and at 

 Glasgow 280 feet. We have calculated, from data which were in- 

 tended to be under-estimates in every case, that there were at least 

 two and a lialf miles of average thickness in what geographers call 

 the great ice-cupola of the south pole. If, therefore, not only this 

 were removed, but an equal quantity of ice were deposited at the north 

 pole, there would be a deepening of the sea at the arctic circle of 

 1,500 feet. 



Thus it is seen that, as certainly as terrestrial revolutions continue, 

 in the course of 10,000 years there must come an entire reversal 

 of polar conditions. The southern waters must be drained off to make 

 the oceans of an opposite hemisphere. New lands, enriched with the 

 sediment of a hundred centuries, will rise up to extend the borders of 

 the old south continents, and islands joining together, will expand 

 into mainlands. At the same time the northern continents must be in 

 great part submerged, and their summits and ranges become the bleak 

 islands and the bold headlands of a tempestuous ocean. Central 

 Asia, with its broad table-lands, may still retain the name of a con- 

 tinent; but, beyond a few outlying islands, there will be no Europe, 

 and but little of North America left. The Atlantic waters will stand 

 five hundred feet over Lake Superior, and will wash the base of the 

 Rocky Mountains in all their length. A new Gulf Stream may again, 

 as it must often have done before, flow up the valley of the Mississippi, 

 returning the deltas to the prairies, and remaking the beds of the gar- 

 den of the world. These are no idle or impossible fancies. Not only 

 are they the results of rigorous calculation, but they accord perfectly 

 with the unmistakable evidences Avhich the ocean has left, all over our 

 land, of its recent work and presence. 



The time-honored geologist, Sir Charles Lyell, lays great stress on 

 the quantity of land and the configurations of continents, as chiefly 

 efficacious in the great climatic changes. But it may be pertinently 

 asked, What becomes of his continents and configurations when the 

 seas of one pole advance to the other, as they unquestionably do, as 

 they cannot but do, every 10,500 years, obedient to the transfer of 



' This article was written before the publication of Mr. Croll's recent work on "Cli- 

 mate and Time," The reference here is to an article published some years since in the 

 Philosophical Magazine. 



