EEELEVATION FOLLOWING THE ICE DEPARTURE. 507 



finds evidence of snbmerg'ence to tlie amount of 200 or 300 feet, while the 

 glacial conditions still endured.^ 



KEELEVATION CLOSELY FOLLOWING THE DEPARTURE OF THE ICE-SHEET. 



From the Champlain submergence this continent, since the ice weight 

 depressing it was removed, has been uplifted to its present height. The 

 changes in the levels of the beaches of Lake Agassiz prove that in the 

 interior of the continent this movement closely followed the recession of 

 the ice; but on the shores of Hudson Bay the reelevation is still in prog- 

 ress, indicating that no long time has passed since large remnants of the 

 ice in that region melted away. On the Atlantic coast we have different 

 evidence of the rise of the land soon after the ice-sheet disappeared, and 

 the movement there, as also on the coast of British Columbia, resulted in 

 an elevation somewhat higher than now, so that the latest oscillation of 

 these regions has been a subsidence, which is still very slowly continuing. 



The recent depression of the eastern seaboard is shown by submarine 

 stumps of trees, rooted where they grew, and by submerged peat bogs, 

 which prove that the wliole coast from New Jersey to southern Greenland 

 has lately sunk to a moderate extent. The maximum known l)y these 

 observations is about 80 feet, at which depth a peat bed occurs under the 

 Tantramar salt marsh at the head of the Bay of Fundy." After the land 

 had recovered from the Champlain depression to its present level, or per- 

 haps to the higher stage noted, the temperature of the North Atlantic was 

 for a time somewhat warmer than now. Southern species of marine mol- 

 lusks were then able to extend northward to the Gulf of St. Lawrence; 

 but they have since become exterminated by a considerable refrig eration of 



■Geol. and Nat. Hist. Survey of Canada, Report of Progress for 1878-79, p. 95 B. Trans., Royal 

 Society of Canada. Vol. VIII. Sec. IV, 1890, pp. 3-74. Important notes of recent changes m level of 

 the coast of British Columbia, of the State of Washington, and of soutliern Ahiska, are given by 

 Dr. Dawson in the Canadian Naturalist, new series, Vol. VIII, pp. 241-248, April, 1877. He concludes 

 that this area had a preglacial elevation at least about 900 feet above the present sea-level during 

 part or the whole of the Pliocene period, this being indicated by the fjords; that it was much 

 depressed during the Glacial period; .and that in Postglaci.al time it lias been reelevated to a height 

 probably 200 or 300 feet greater than now. followed by subsidence to the present level, the Latest part 

 of this oscillation being a somewhat rapid depression of perhaps 10 or 15 feet during the latter part of 

 the last century— a movement which may still be slowly going on. 



^Geol. and Nat. Hist. Survey of Canada, Annual Report, new series, Vol. IV, for 1888-89, pp. 4. A 

 and 10 N. 



