486 THE GLACIAL LAKE AGASSIZ. 



showed that tlie movement of elevation of tlae country at Lalce Traverse 

 after the ice alioA^e was meked probably did not exceed 90 feet; that thence 

 northward the rise of the land and sinking of the geoid level, as affected by 

 ice attraction, increased to a combined value of about 350 feet at Gladstone 

 and nearly 500 feet in the district of the northern part of Duck Mountain, 

 where, as in North Dakota and Minnesota, the maximum rate of ascent of 

 the beach planes is toward the north-northeast; and that probably thence 

 north to the Saskatchewan and the Churchill, northeast to Hudson Bay, 

 and east to Jame%s Bay, the Ottawa basin, and Montreal, the amount of 

 uplift, since the departure of the ice, of a very large central part of the 

 area which it had covered was somewhat uniforndy 500 to 600 feet. It 

 has been also shown from Mr. Tp-rell's observations in the district of Riding 

 and Duck mountains that after the southern half of the lake area had been 

 raised almost to its present height, and while that country north to Glad- 

 stone lay nearly undisturbed, a great uplift of later date took place in 

 the next 100 miles to the north; and that, after both these movements, the 

 region of Hudson and James bays was still later raised, probably from its 

 maximum dej)ressiou to its present height. Throughout the area of my 

 survey of the Lake Agassiz shore-lines, and northward along the Riding 

 and Duck mountains, the epeirogenic movement was a tilting with ascent 

 to the north-northeast, toward the region where the ice-sheet had its greatest 

 thickness; but the more northern and northeastern part of this lake bed, 

 with a great adjoining central portion of the vast expanse which had been 

 ice-enveloped, were elevated to an approximately uniform amount. The 

 elevation progressed from south to north and northeast like a wave, per- 

 manentl)- uplifting successive areas, excepting so far as tlie borders of each 

 necessarily shared in the movements of the contiguous tracts earlier or later 

 uplifted. 



CHANGES OF IjEVELS NEARI^Y COMPLiETED DURING THE EXISTENCE 

 OP LAKE AGASSIZ. 



Nearly the entire amount of the changes in the levels of the beaches 

 of Lake Agassiz was evidently contemporaneous with the existence of this 

 lake, taking place gradually, but apparently progressing comparatively fast 



