146 PROCEEDINGS OF THE ALBANY MEETING 



A large part of the uplift took place during the existence of the later lake, 

 and a large area beyond the margin of the ice-sheet was affected. If the 

 uplift was due to isostatic recovery following relief from the burden of the 

 ice-sheets, as is generally held, it is evident that uplift must have "lagged" 

 behind the removal of the main mass of the Wisconsin ice-sheet. 



Discussion 



Prof. Fkank Lkvkhett spoke of the importance of the work of Mr. Johnston 

 in throwing light on the closing part of the Wisconsin stage of glaciation, and 

 especially in its suggestion of a second or later l^ake Agassiz, formed by a re- 

 advance of ice from the northeast which blocked the drainage to Hudson Bay. 

 The first Lake Agassiz loses none of its importance, however, because of the 

 recurrence of the ponded condition in the Lake Agassiz area. It is probable 

 that the southern outlet through the Minnesota Valley, known as River War- 

 ren, was cut nearly to its full depth by the discharge from the earliest lake. 

 Mr. Warren Upham's interpretations, as given in the monograph on the Glacial 

 Lake Agassiz, seem, therefore, to need merely a supplementary chapter rather 

 than a i-adical modification. 



The Secretary read a letter from Warren Upham as follows : 



"It is quite evident that W. A. Johnston, of the Canada Geological Survey, 

 has a strong 'courage of his convictions' for his papers on Lake Agassiz ; but I 

 feel entirely sure that his main contention is an error, and I hope that good 

 discussion by members present, following his paper, and also after Keyes' paper 

 on Lake Bonneville, will adequately defend whatever there is of truth of Gil- 

 bert's and my United States Geological Survey monographs. 



"The grand evidence that the melting ice-sheet lay close against each side 

 of Lake Agassiz, while it grew from south to north, is the derivation of the 

 sand and gravel of the great deltas on the east and the much greater deltas 

 on the west, these deposits being surely supplied in such localized abundan(;e 

 by drainage from the drift-covered melting ice-border. 



"It is objected that the lake area should show boulders dropped from bergs, 

 but I believe that the melting in rapid progress by surface ablation of the ice- 

 sheet gave no conditions for detachment of bergs." 



Mr. J. B. Tyrrell : It gives me much pleasure to know that the work which 

 Mr. Warren Upham and I did some years ago on Lake Agassiz is now being 

 followed up, and I trust that it may be Mr. Johnston's good fortune to continue 

 to study and elucidate the history of this great postglacial lake, not only in 

 its higher stages, when it discharged southward, but in its lower stages of 

 growth and decline, when it discharged into or was connected in some way 

 with the arctic waters of Hudson Bay. 



During the past summer I had the opportunity of traveling over the Hudson 

 Bay Railway from The Pas, on the Saskatchewan River, to mile 295, which 

 was as far as the rails were laid at that tirde, and some brief notes of the 

 Lake Agassiz deposits observable along the line of the railway may be of inter- 

 est here. 



The town of The Pas is built on a strong gravel ridge, one of the old shores 



