THE POLAR GLACIERS. 27 



on the 21st day of June, our summer solstice. In the period 

 comprising the first case, 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 rigorous 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 differences there may be between the two hemi- 

 spheres, 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 

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

 and at Glasgow 280 feet. We have calculated, from data which 

 were intended to be under-estimates in every case, that there 

 were at least two and a half 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 con- 

 tinue, 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 sub- 

 merged, and their summits and ranges become the bleak islands 

 and bold headlands oi. a tempestuous ocean. Central Asia, with 

 its broad table-lands, may still retain the name of a continent ; 

 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 w r ill 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 re- 



* The reference here is to an article published some years since in the Philosophical Magazine. 



