WA VE-LIKE PROGRESS OF AN EPEIROGENIC UPLIFT. 3 8 5 



but onl}^ to a comparatively small amount, from 200 to 500 or 

 .600 feet, after the departure of the ice-sheet. In Scandinavia, 

 according to the investigations of Baron de Geer, the postglacial 

 uplift has varied from a minimum of 100 feet or less at the 

 southern extremity of Sweden, to a maximum exceeding 1,000 

 feet in the central part of the peninsula/ Likewise in South 

 America, along a distance of 1,200 miles, from the Rio Plata to 

 Tierra del Fuego, the land has been elevated since its glaciation, 

 the general extent of this movement in Patagonia, as observed 

 by Darwin, being between 300 and 400 feet.^ 



The special case of an epeirogenic movement progressing like 

 a wave, which it is the purpose of this paper to consider, is this 

 latest, moderate uplift of North America, and especially of its 

 central belt comprised in the Mississippi and Nelson river basins, 

 from its depression at the close of the Glacial period. While the 

 ice-sheet was retreating, this great area was rising Ss fast as its 

 burden was removed. Close upon the wasting ice-border there 

 followed a wave of permanent uplift of the land on which it had 

 lain. First the loess district along the Mississippi and the upper 

 part of this basin were elevated ; next, the southern half of the 

 area of the glacial lake Agassiz ; later, its northern half ; and last 

 of all, the country enclosing Hudson bay, with which also was 

 probably associated, as very late in its uplift, the region of the 

 great Laurentian lakes, including lake Champlain, and of the 

 Ottawa and the St. Lawrence. From south to north and north- 

 east the wave of elevation advanced, and, according to Dr. 

 Robert Bell, the rise of the land has not yet ceased about James 

 and Hudson bays, where, in the central part of the glaciated 

 region, we must suppose that the ice-sheet had its greatest 

 thickness and was latest represented by lingering remnants. 

 Having thus outlined our theme, let us return and look more 



' Bulletin, Geol. Soc. Am., Vol. 3, 1891, pp. 65-68, with map of the late glacial 

 marine area in southern Sweden; Proceedings of the Boston Society of Natural 

 History, Vol. 25, 1892, pp. 456-461 (also in the Am. Geologist, Vol. n, pp. 23-29, 

 Jan., 1893). 



= "Voyage of H.M.S. Beagle," chapter viii. 



