512 W. UPHAM STAGES OF THE ICE AGE 



what higher than now, and its latest movement from Few Jersey to south- 

 ern Greenland has been a moderate depression. The vertical amount of 

 this Postglacial elevation above the present height, and of the recent 

 subsidence, on the coast of New Jersey, New England, and the eastern 

 provinces of Canada, is known to have ranged from 10 feet to a maximum 

 of at least 80 feet at the head of the Bay of Fundy, attested in many 

 places by stumps of forests, rooted where they grew, and by peat beds 

 now submerged by the sea. As in Scandinavia, the restoration of isostatic 

 equilibrium is attended by minor oscillations, the conditions requisite for 

 repose having been overpassed by the early reelevation of outer portions 

 of each of these great glaciated areas. The end of the Ice Age was not 

 long ago, geologically speaking, for equilibrium of the disturbed areas 

 has not yet been completely attained. 



Estimated Time Ratios 



In correlating our continental glaciation with the two stages of high 

 water of Lake Bonneville, as noted by Gilbert, Nebraskan time appears 

 to have far exceeded the combined Kansan, Illinoian, lowan, and Wis- 

 consin glacial stages, in a ratio of not less than five to one. The Afto- 

 nian stage, when the border of the ice-sheet melted over wide areas, but 

 afterward advanced even beyond its previous extent, probably coincided 

 with the long time when Lake Bonneville was reduced by evaporation to 

 an area similar to the Great Salt Lake, or may indeed have been wholly 

 dried up, that time of desiccation having been longer than the Postglacial 

 period. 



The latest Wisconsin stage, with the formation of its many recessional 

 moraines, saw the ice-sheet gradually melted away. Since the retreat 

 of its border from central Minnesota, the Mississippi River has eroded its 

 gorge below the Falls of Saint Anthony, which Prof. N. H. Winchell, by 

 comparing its recent rate of erosion with the length of the gorge, esti- 

 mated to have required about eight thousand years. Similarly the 

 Niagara Falls and gorge supply evidence, according to (<. K. Gilbert, 

 Prof. G. F. Wright, and the present writer, that the northward recession 

 of the ice-border uncovered the region of Lakes Erie and Ontario about 

 seven thousand years ago. These measures of late Glacial and Post- 

 glacial time in America accord well with recent surveys by Baron De Geer 

 in Sweden, where the last twelve thousand years have witnessed the limit- 

 ing of the latest part of the European ice-sheet. 



During the early part of the time represented by erosion of the Saint 

 Anthony gorge, the later seven marginal moraines in the series of twelve 



