306 THE ICE AGE IN NORTH AMERICA. 



were likewise greatly enlarged by the damming up of outlets 

 which formerly conducted their waters southward into the 

 Mississippi. These barriers also turned the surplus waters 

 of those inland seas toward the east. The outlet of Lake 

 Superior through the rapids of the Sault Ste. Marie is caused 

 by the increased depths of the glacial deposits to the west 

 across the narrow isthmus separating it from Lake Michigan, 

 where, doubtless, a ship-canal could be cut between these two 

 lakes without encountering any rocks at all. From the south- 

 ern end of Lake Michigan, also, a deeply-buried preglacial 

 channel is believed to run southwest, through Kankakee, 

 Livingston, and MacLean counties, toward the Mississippi. 



Professor Newberry's theory ot the eastward preglacial 

 drainage from the region of Lake Ontario meets with insuper- 

 able difficulties, notwithstanding the apparent support it 

 would receive from the startling facts recently brought to 

 light concerning the depth of the preglacial trough of the 

 Hudson River, where the engineers sounding for a foundation 

 for a conduit to convey water from the Catskill region to 

 New York City in 1906, found that a short distance above 

 West Point the rock bottom of Hudson River was 487 feet 

 below the present bottom. The depth of the buried channel 

 between New York and Newark is not certainly known, but 

 the numerous railroad tunnels under the river are uniformly 

 through unconsolidated sedimentary deposits, and in case 

 of the Pennsylvania road abutments are sunk to a consider- 

 able depth in the mud to support the tunnel, as if it were a 

 bridge. Outside the harbor of the city this preglacial outlet 

 has been traced by the sounding line of the Coast Survey for a 

 distance of a hundred miles, to the edge of the deep water of 

 the Atlantic. .Over a considerable portion of this distance it 

 has a width of more than a mile and is 2,000 feet deep. These 

 facts concerning the Hudson, brought to light since Professor 

 Newberry's death would have greatly strengthened his 

 argument. There is, however, one fatal objection to his con- 



