354 POPULAR SCIENCE MONTHLY. 



CAUSES, STAGES, AND TIME OF THE ICE AGE. 



By WARREN UPHAM. 



IF we could see the entire earth at once, by some grand exten- 

 sion of our range of vision, as we might walk around a geo- 

 graphic globe a hundred feet in diameter, and examine it fully, 

 with comparison of all portions of its area, probably no other fea- 

 tures of the great terrestrial panorama would be so impressive as 

 the wonderful diversity of climatic conditions. At the same time 

 with perpetual summer on the equator and throughout nearly all 

 of the intertropical zone, a wintry covering of snow and ice would 

 be seen on all lands in high latitudes about one or the other pole. 

 While every bounty of luxuriant plant and animal life is present 

 to attract the traveler and furnish him sustenance in the central 

 zone, the rigorous climate which is gradually encountered in 

 approaching the poles, and the general decrease and limitation of 

 both flora and funa, have opposed insuperable obstacles to the 

 most eager and courageous explorers. About four hundred and 

 fifty miles at the north, and about eight hundred and fifty miles 

 at the south, lie beyond the farthest limits of exploration ; and 

 more than double these distances must be crossed, respective- 

 ly, if one would pass, according to Nansen's hope and plan, 

 from one side to the other of the hitherto untraversed circum- 

 polar areas. 



During the Ice age, or Glacial period of geology, very exten- 

 sive and thick sheets of land ice, like those now enveloping the 

 Antarctic continent and the interior of Greenland, overspread the 

 northern half of North America (excepting the greater part of 

 Alaska) and northern Europe, with nearly the whole of the Brit- 

 ish Isles. The southern boundary of the North American ice 

 sheet crossed Nantucket and Martha's Vineyard, Block Island, 

 Long Island, and Staten Island. On the mainland it extended 

 through northern New Jersey and northeastern and northwestern 

 Pennsylvania, being indented by a great angle, whose apex was at 

 Salamanca in southwestern New York. Thence it reached south- 

 west and west across southern Ohio, Indiana, and Illinois, and 

 through central Missouri, into northeastern Kansas ; and beyond, 

 it curved far northward, crossing eastern Nebraska and South 

 and North Dakota. From near Bismarck it again trended west- 

 ward through Montana, Idaho, and Washington, to the Pacific 

 Ocean not far south of Puget Sound. North of this line an 

 area of about four million square miles, stretching to the Arctic 

 archipelago, was covered with ice hundreds and thousands of 

 feet deep. 



The comparatively small present ice sheet of Greenland covers 



