54 NEW YORK STATE MUSEUM 



material; and probably there was also upturning of the bottom ice 

 layers so that these deposited their burden of debris on the inner side 

 and on the crest of the moraine during its upbuilding. 



The major portion of the material comprising the visible structure 

 of the moraine seems to have been debris carried in the upper layers 

 and on the surface of the ice lobe and aided in attaining its final 

 position on the moraine in some degree by water transportation. 

 Enormous volumes of water were continually being freed by the ice 

 melting, not only at the lobe-end but also for a considerable area 

 back from the front. Accordingly, it is not surprising to find that 

 the superficial portions of the moraine are largely made up of water- 

 sorted materials, sand and gravels coarsely stratified. On this ac- 

 count, too, the moraine, especially on its west side, has a distinctly 

 kame structure. On the east side where the view shown in plate 4 

 was made, a much more characteristically ice-deposited hummock 

 surface is found, and the cultivated field of the foreground of this 

 picture shows the typical boulder-clay composition of such accumu- 

 lations. 



Kame kettles and hummocks. In a kame moraine the knobs 

 and kettles are typically much more conspicuous than the similar 

 hills and hollows resulting from direct ice-deposit of the glacial 

 debris. The Tully moraine on its west side, as has been noted, has a 

 kame structure and it also exhibits, especially along its south front, 

 very strikingly and characteristically the knob and kettle topography 

 of such accumulations. Indeed, few finer examples of this phenom- 

 enon could be found in all the accumulations of continental glaciation 

 than occur in this section of the Tully moraine. 



In origin the kettle or hollow, rather than the knob, is the deter- 

 mining factor of such topography, and the history of these hollows 

 is another significant link in the chain of evidence connecting all the 

 phenomena found in the region with the glacial invasions. As the 

 moraine accumulated, deposit along the front of the ice was fre- 

 quently much more rapid than the melting of the ice of a particular 

 area. Hence it commonly happened that a block of ice was buried 

 deeply under the gravelly debris. In such position it was effectively 

 protected from melting as quickly as did the exposed ice areas ad- 

 jacent to it. In time the buried block was completely detached from 

 the ice tongue and persisted, unmelted, while additional masses of 

 deposit were piled around and over it. When the detached ice blocks 

 finally melted away completely the deposits over it must have sunk 

 down to fill the cavity thus created. Such burial, melting and slump- 

 ing must have constantly occurred while the moraine was forming, 



