ANCIENT WATER LEVELS OF CH A MPLAIN— HUDSON VALLEYS 95 



before tlie moraines, when the ice ran to the south, the direction 

 of ice motion had scarcely changed at this locality during the 

 retreat from the terminal moraine. 



West of Tappan in New Jersey other frontal deposits similar 

 in form to the morainal ridges at this place occur in the form 

 of a crescent open on the north, indicating the position of the ice 

 front at this stage in that direction. 



The extension of the ice front east of the Hudson at this stage 

 is not clearly shown by any facts now at hand. 



The moraines at Tappan X. Y. and in Harrington X. J. appear 

 by their alinement to be synchronous deposits. The water-laid 

 drift confronting the Tappan deposits rises to GO feet above sea 

 level, but the plains confronting the Harrington deposit appear 

 to rise to 100 feet. It is evident that these slopes of washed 

 drift were not controlled by one and the same water level. Slop- 

 ing plains and fans of drift are built up along certain ice fronts 

 and along the flanks of gullied mountains, independently of water 

 levels, to quite different altitudes above the stream beds at their 

 base. Jt is therefore legitimate to suppose that these deposits 

 may also have developed without regard to sea level or lake level, 

 so that the sea level of the time may have been at or below the 

 level of the lowest of these diluvial fans. 



Kyack terraces preglacial (pre-Wisconsin ) . There are two well 

 marked terraces in the vicinity of Nyack on the west bank of the 

 Hudson, but these are so many benches formed by the Triassic 

 sandstones outcropping beneath the Palisade trap sheet. They 

 are everywhere except in the southern part of Nyack covered by 

 glacial till. The lowest of these terraces is about 80 feet above 

 sea level. The red sandstones crop out in a low bluff on the 

 water's edge south of the village. The upper terrace is strongly 

 marked between 180 and 200 feet and corresponds closely to the 

 rock terrace of the Hudson at many points. Another less 

 extensive terrace occurs south of Hook mountain between 280 

 and 300 feet. 



On these terraces the drift is largely reddish till derived from 

 the red sandstone and shale. For about 50 feet above sea level 

 the surface drift is grayish and clayey, as if the ice had smeared 

 earlier glacial clays over the rock benches. 



