No. 7.] DANA — DISCHARGE OF LAKE WINNIPEG. -i^l 



We may infer also, from the near correspondenec between 

 the northward slope of the lake bottom prairie and th it of the 

 bordering plateaus, that the prairie and plateiu were affected 

 alike by the conditions as to level. And we may deduce from 

 the regularity of the slope, that the conditions as to level 

 affected equally the region from Lake Traverse to Lake Win- 

 nipeg, and beyond doubt also to u much greater undetermined 

 distance northward. 



This conclusion bears so profoundly on questions as to the 

 condition of the earth's interior, and the ori"'in of chan"es of 

 level over the earth's surface, that it is o;reatlv to be desired 

 that liirther investigation should place the facts beyond all 

 doubt. 



Admitting that the facts are correctly given, they appear to 

 point to the following succession of events: 



The fact that the lake deposits are underlaid by unstratitied 

 drift, shows that before the era of the uTeat lake the ojacier had 

 moved southwestward over the region, and deposition ot moraine 

 material had taken place. The high-level prairie either side of 

 the lake region and of the Minnesota valley is made largely of 

 this unstratified drift ; but the generally level surface in the 

 part toward lake region and valley, and the stratification in much 

 of the material, are evidence that the floods from the meltine: 

 glacier covered and levelled it, and stratified its bedded deposits; 

 the coarseness of these deposits, and the large size of the valley 

 of dischai'ge, that the flood waters had great velocity; the height 

 of the prairie, that they stood 100 to 150 feet above the present 

 level of the region including Lake Traverse, instead of the 40 

 feet at the divide above supposed. This time of maximum flood 

 and of rather violent fluvial conditions was followed by the era 

 of the Great Lake, that is of quiet waters and lacustrine deposits, 

 with slow discharge over the Lake Traverse region ; which may 

 have been brought about in {)art by diminished supply of waters 

 from the melting ice and precipitation, but more, with little 

 doubt, by a diminution in the slope of the general surface, which 

 was a part of the great change of slope tliat went on, as explained 

 by General Warren, until the land was reduced to its present 

 pitch and the streams to their modern courses. 



The application of a new name, Lake Agassiz, to the flooded 

 Lake Winriipeg, proposed by Mr. Upham because of its alleged 

 relation to the retreating ice-sheet, tends to obscure the great 

 Vol. X. cr No. 1. 



