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NEW YORK STATE MUSEUM 



half a century by numerous observers whether amateurs or official 

 geologic surveyors has failed to bring to light postglacial marine 

 fossils above the level of the sea at the mouth of the Hudson. 



The comparison of the extreme ends of the great Hudson-Cham- 

 plain depression speaks eloquently of marine submergence on the 

 north during a time when the region on the south about the mouth 

 of the Hudson at least was as it now is above the level of the sea. 



SUMMARY OF GEOLOGIC HISTORY BEGINNING WITH THE RETREAT OF THE 

 WISCONSIN ICE SHEET 



From the foregoing more or less detailed but as yet incomplete 

 account of the successive frontal moraines in the Hudson and 

 Champlain valleys, it follows that the ice front after receding 

 from the moraine at New York Narrows became more and more 

 irregular in outline, more and more reduced to a long loop pro- 

 jecting southward in the Hudson valley and receding northward 

 over the highlands which formed a wall on either side of it. When 

 the ice had so far dwindled away as not to be able to surmount 

 the Archean ridge of the Highlands, it still pushed southward 

 through the Hudson canyon in this elevated district a narrow 

 tongue of ice which has left its marginal deposits of stratified 

 gravel, sand and clay, at Croton Point, North Haverstraw, about 

 Peekskill, and in the vicinity of West Point. During this stage 

 of the waning Wisconsin epoch, the land from the Highlands 

 southward through the lower Hudson valley appears to have been 

 occupied by standing water about the margin of the receding ice. 

 The level of this body of water is now marked by proglacial deltas 

 which rise to the north at the rate of about 2.6 feet a mile; 1 an 

 inclination very close to that found by Kummel for the shore lines 

 of Lake Passaic in New Jersey. 



When the ice disappeared from the Wallkill valley about the 

 northern slopes of the Highlands, it formed a long tongue from 

 Newburg northward covering the greater part of the width of the 

 floor of the Hudson valley. About its margins were accumulated 

 stratified gravels and sands now in the form of terraces, with ket- 

 tles and ice-block holes, extending on its eastern margin north- 



a This estimate is obtained by taking the distance, 34.5 miles, from the 

 College Point delta with an elevation of 30 feet, to the terrace used for a 

 state military camp at Peekskill with an elevation of 120 feet. 



