190 THE GLACIAL LAKE AGASSIZ. 



to the extent of a third or half of their depth by the glacial drift. The 

 erosion of the valley, therefore, must have fallen far short of supijh'ing 

 the material of the Assiiiiboine delta, not to mention the fine silt and 

 clay which were carried into the lake beyond the gravel and sand delta 

 and may be of equal volume. Probably at least half of these lacustrine 

 deposits were modified drift l^rought down by streams from the melting 

 ice-sheet on the upper Assiniboine basin, north of the mouth of the Qu'Ap- 

 pelle, and swept forward by the strong current of the ri^er until it reached 

 Lake Ag-assiz. 



INFLUENCE OE ADJOINING LAKES OR THE SEA ON THE DEPOSI- 

 TION OF THE DRIFT. 



From Nantucket and Cape Cod northeastward the ice-sheet, at its 

 greatest extent and during a considerable part of its time of recession, 

 terminated in the ocean. In the interior of the continent, too, it was 

 bounded during its recession b}^ vast lakes filling the basins that are now 

 partly occupied by the great lakes of the 8t. Lawrence, Nelson, and Mac- 

 kenzie rivers. During all ray examination of the shore-lines, deltas, and 

 bed of Lake Agassiz I have carefully studied the effects attributable to 

 the influence of this lake on the deposition of the di-ift, comparing its area, 

 the valley of the Red River of the North, with other portions of Minne- 

 sota, South and North Dakota, and Manitoba, which had a land surface 

 during the departure of the ice. Other glacial lakes of smaller size in 

 these States and this Canadian province have also come under my obser- 

 vation, besides portions of the drift deposited in the glacial precursors of 

 the Laurentian lakes; and on the Atlantic Coast I have made a detailed 

 examination of the marine drift of southeastern New Hampshire. The 

 more southern parts of the New England seaboard'Avhich I have similarly 

 examined, including the coast from Boston to Plymouth, Cape Cod, Nan- 

 tucket, Marthas Vineyard, the Elizabeth Islands, Block Island, and Long 

 Island, appear to me to have stood at their present height or somewhat 

 liio-her during the maximum extension and the recession of their broad 

 eastern lobe of the ice-sheet. 



