86 NEW YORK STATE MUSEUM 



like those north of Pat pond and east of Boreas river or at the 

 summit of Beech hill, clearly prove the failure of the topography 

 to determine the direction of the ice movement. 



Ice Erosion 



There is no evidence that the ice was a vigorous agent of erosion 

 within the quadrangle. It may possibly have scoured out and 

 somewhat deepened the basin of Schroon lake, but definite proof 

 is lacking. Certainly none of the more prominent valleys were 

 produced by ice erosion, for, as above shown, the main body of 

 the ice flowed across the trend of the valleys rather than parallel 

 to them as would have been necessary for ice erosion to have been 

 very effective for their development or even notable modification. 



It is quite certain, however, that the ice did remove from its 

 original position practically all the preglacial soils and most of the 

 rotten rock. Further, the vast number of glacial pebbles and 

 boulders of comparatively fresh rocks clearly show that much 

 relatively fresh rock must have been removed probably by the 

 process of plucking or pushing ofif joint blocks which during trans- 

 portation became more or less rounded. Altogether, however, the 

 total amount of material eroded by the ice made no marked dif- 

 ference in the preglacial topography. The dumping of glacial 

 material in the valleys during and after the ice retreat has probably 

 altered the topography more than erosion by the ice. 



Glacial Deposits 



Morainic deposits. Typical morainic deposits, mostly glacial 

 till or ground morainic material, are common throughout the quad- 

 rangle though usually they are more or less associated with strati- 

 fied or fluvio-glacial materials. Boulder clay is seldom seen. 

 Morainic deposits are particularly well developed over the lower 

 lands or valleys, while well up on the hills and mountains they are 

 usually absent or thin. It is evident that, during the retreat of 

 the great ice sheet, the burden of morainic material was largely 

 dumped in the valleys either by direct deposition from the ice or by 

 water in connection with the ice, or both. 



The most extensive development of morainic and fluvio-glacial 

 deposits is in the area of over 6 square miles mapped as Pleisto- 

 cene in the central portion of the quadrangle. Within this area 

 the hard rocks are everywhere concealed under glacial deposits 



