264 THE GLACIAL LAKE AGASSIZ. 



harbor of New York may probably have been once 50 or 60 feet in its 

 leuglh of about 100 miles. Before the time of disappearance of the ice- 

 barrier at Quebec this descent may have been diminished, or the seaboard 

 at New York may have sunk so as to bring the shore-line nearly to its 

 present position ; but the Hudson Valley meanwhile had been uplifted, so 

 that an outflow from Lake St. Lawrence crossed the low divide, now about 

 150 feet above the sea, between Lake Champlain and the Hudson. This 

 is known by the extension of fossiliferous marine deposits along the Lake 

 Champlain basin nearly to its southern end, while they are wholly wanting 

 along all the Hudson Valley. Indeed, the outflowing river from Lake St. 

 Lawrence or the Hudson during the subsequent postglacial epoch chan- 

 neled the lt)wer part of this valley to a depth of about 100 feet below the 

 present sea-level, proving that the land there, as Merrill points out, stood 

 so much higher than now during' some time after the ice retreated. 



When Lake Iroquois ceased to outflow at Rome, and after intervening 

 stages of outlets existing for a shoi't time at successively lower levels north 

 of the Adiroudacks began to occupy the Lake Champlain basin, outflowing 

 thence to the Hudson, its surface fell by these stages about 250 feet to the 

 glacial Lake Hudson-Champlaiu, which had doubtless reached northward 

 along the whole length of the Champlain basin. The level of the resulting 

 Lake St. Lawrence at the later time of ingress of the sea past Quebec fell 

 probably 50 feet or less to the sea-level. During these changes the out- 

 flow of Lake Agassiz may have passed in the ways before described to 

 the sea through the Hudson, and afterward to the enlarged Grulf of St. 

 Lawi'ence, if the sea had not 2)reviously come into Hudson Bay. 



LAKE MINNESOTA. 



Before Lake Agassiz commenced to exist, the receding Minnesota and 

 Dakota lobes of the ice-sheet had each given place to a large lake on the 

 central part of the area from which they withdi-ew. By the barrier of 

 the Minnesota ice-lobe a lake having an elevation of about 1,150 feet 

 above the sea was formed in southern Minnesota, in the basin of the 

 Blue Earth and Minnesota rivers, outflowing southward by way of Union 

 Slough to the East Fork of the Des Moines. In its maximum extent this 

 lake probably had a length of 160 miles, from Waseca to Big Stone Lake, 



