PLEISTOCENE MARINE SUBMERGENCE 63 



shore as far northward as Alexandria Bay and Redwood, in a 

 partial way, as the beaches are detached and mostly weak (163, 

 plates 44-47; pages 136-72). The most important series of bars 

 is on a moraine tract 2 miles north of Lafargeville, with summit 

 altitude about 440 feet. In this district of horizontal rocks, low 

 relief and clay plains; or farther north, with glaciated granitic 

 knobs and silted hollows, the waves found little material and poor 

 conditions for leaving their inscriptions. 



SUMMARY 



It seems possible that the Pleistocene history of New York 

 State includes more than one ice invasion, or glacial epoch ; but 

 this writing deals with only the records of the latest ice sheet, and 

 specifically with the waters that occupied the low valleys as the 

 ice body melted. 



When the Labradorian ice cap was disappearing, the land which 

 had been beneath the ice sheet was much lower than at present. 

 The amount of the depression seems to bear quite direct proportion 

 to the thickness and weight of the ice burden. The measure of 

 that depression is found in the Hudson-Champlain valley, and 

 about New York City and over Long Island, in the shore phenomena 

 left by the sea-level waters that took possession as the ice vacated. 

 The amount of the land uplift is shown in the maps, and for the 

 Hudson-Champlain valley in the diagram, plate 10. 



In the St Lawrence-Ontario valley the amount of postglacial 

 rise of the land is found by the amount of deformation, or north- 

 ward up-tilting of glacial lake shore lines, which must have origi- 

 nally been horizontal. The shore line of Lake Iroquois has been 

 deformed 668 feet, and bodily lifted J2 feet more, which gives a 

 total rise at Covey hill of 740 feet, the same as the altitude of the 

 marine beaches at that point. The diagram (plate 11) shows the 

 tilt of the St Lawrence beaches. 



The records of the sea-level waters in the Hudson-Champlain 

 valley cover all of the long time involved in the wamng and dis- 

 appearance of the ice sheet, from the moment of its greatest extent 

 to the time when it passed entirely off the State. But the glacial 

 records in the St Lawrence valley cover only the latter part of 

 glacial time. For this writing the history of the St Lawrence 

 valley is only that of Iroquois and Post-Iroquols time. 



The history, in brief, is as follows. The sea-level waters con- 

 tinuously laved the receding front of the glacier as it retreated up 

 the Hudson and Champlain depression. Large glacial boulders in 



