358 THE ICE AGE IN NORTH AMERICA, 



was a shoulder of the Alleghanies, too high and too rugged to 

 be buried under a continuous ice-sheet; but its whole front 

 was worn away for a hundred miles or more, and it was deeply 

 creased where now we see the peculiarly elongated lakes of 

 New York, and cut through in certain gaps, to the valley of 

 the Delaware. In Ohio the erosion was easier and carried far- 

 ther south. The barrier was also lower, and was finally over- 

 topped by one great lobe of ice, which flowed on to the south 

 and west until its edge reached the Ohio River. . . . 



With the amelioration of the climate the wide-spread ice- 

 sheets of the period of intensest cold became again local gla- 

 ciers, which completed the already begun work of cutting out 

 the lake-basins. At first, the glacier which had before flowed 

 over the water-shed in Ohio was so far reduced as to be unable 

 to overtop its summit; but, deflected by it, it flowed along its 

 base, spending its energies in cutting the shallow basin in 

 which Lake Erie now lies. 



A further elevation of temperature curtailed the glacier 

 still more, and Lake Erie became a water-basin, while local 

 glaciers left from the ice-sheet excavated the basins of Lake 

 Michigan, Lake Huron, and Lake Ontario. The latter lake 

 was apparently formed by the same glacier that made the Erie 

 basin, but when much abbreviated. It flowed from the Lau- 

 rentian Hills and the north slope of the Adirondacks, and was 

 deflected by the highlands south of the lake-basin, so that its 

 motion was nearly westward. This chapter in the history of 

 our lakes was apparently a long one, for Lake Superior, Lake 

 Michigan, Lake Huron, and Lake Ontario are all of great 

 depth. 



The melting of the glaciers was accompanied, perhaps 

 occasioned, by a sinking of the continent, which progressed 

 until the waters of the Atlantic flowed up the valley of the St. 

 Lawrence to Kingston, and up the Ottawa to Arnprior (Daw- 

 son). The valleys of the St. Lawrence and the Hudson were 

 connected by way of Lake Champlain, and thus the highlands 

 of New England were left as an island. It is also possible that 

 the sea-water penetrated to the lake-basin through the valley 

 of the Mohawk and through that of the Mississippi, but of 

 this we have no evidence in the presence of marine fossils in 



