ANCIENT WATER LEVELS OF CHAMPLAIN-HUDSON VALLEYS 79 



the ice pressed southeastwardly over the state line into Massa- 

 chusetts. Pressing southward through the Hudson valley the 

 Highlands must again have profoundly influenced the movement 

 of the ice both in its retreat and in its advance. The ice passed 

 through the Highland gorge leaving a characteristic glaciated 

 topography in the smoother northern slopes of the high ridges 

 which overlook the river and plucking out boulders from their 

 southern slopes, thus giving the frowning cliffs which meet the eye 

 as one ascends the river. The extension of the lowland developed 

 over the soft Hudson slates to the southwest along the northern 

 side of the Highlands would have afforded a passage for the ice 

 in that direction. The ice passing through the Highlands and at 

 the maximum of glaciation over the highest ridges, must have had 

 a relatively rapid motion through the lower Hudson valley. The 

 axis of this flow passed, as Salisbury has shown by detailed map- 

 ping of the striae, to the west of the Palisade border of the gorge 

 over the Hackensack lowlands of New Jersey. On the west of this 

 line the ice moved southwestwardly over Newark N. J., and on the 

 east of the line southeastwardly over New York city to the mo- 

 raine on Long Island. 



The form of the valley and the Hudson gorge must have influ- 

 enced strongly the retreat of the ice, and many of the glacial de- 

 posits, described in the following pages, demonstrate this point so 

 clearly that, in view of the light which they throw on the several 

 stages of the melting ice as it dwindled away from a complete 

 covering of the eastern part of the State to long tongues of ice 

 comparable to a valley glacier, it becomes possible to outline the 

 history of the retreat in relation to the varying cross-section of the 

 Hudson valley and in regard to the control which the distribution 

 of the ice mass exerted on the character and order 

 ment of deposits made either by the ice in moving deoris to 

 margin, or by the streams which built deposits along that margin. 



THEORETIC MODE OF RETREAT OF REGIONAL GLACIER FROM A VALLEY 



Enough is now known of regional glaciers such as that which 

 spread from the region north of the St Lawrence into New Eng- 

 land and New York to enable us to depict the general mode of 

 retreat of the ice sheet in different districts, having deep meridi- 



