44 W. UPHAM — ^GIANTs' KETTLES ERODED BY MOULIN TORRENTS 



cold waters adjoining glaciers in the arctic regions. As erosion of the 

 bed rock cannot be supposed to have occurred at the bottom of a moulin 

 extending so far below the scale vel, we are compelled to ascribe these 

 glacial potholes, some of them small and others of great diameter and 

 very deep, to some earlier part of the Ice age. I have thought them 

 referable to the time of great continental uplift, proved by submerged 

 valleys, when a severel}'' wintry and snowy climate, resulting from the 

 high land elevation, caused these great areas to become first enveloped 

 by ice-sheets. Afterward, wherever glaciation was interrui)ted and 

 again renewed, previous to the general subsidence of the land which 

 terminated the Glacial period, moulin torrents might erode potholes 

 during the later stage of snow and ice accumulation. Near the coast 

 and at low levels they would lie under the sea during the departure of 

 the ice-sheet, and the washing of sea waves may in some instances have 

 removed the drift with which they had been filled. 



While it is most probable that in some localities, as the Interstate 

 park, giants' kettles originated during the final retreat of the ice, they 

 seem predominantly referable to the beginning of glaciation or to a stage 

 of its renewal. In many places, therefore, the bed rock containing them 

 would be deeply worn away by ensuing glacial erosion, the potholes 

 being spared only where they were protected by deposits of drift or 

 where the rock was little worn by the later glaciation. According to 

 this view, the infrequence of discoveries of these records of moulin water- 

 falls has been due to their present concealment by drift and elsewhere 

 to their erasure by glacial planation of the bed rock. Kames and eskers, 

 on the other hand, belonging to the time of glacial recession and to the 

 surface of the drift, have been abundantly preserved, testifying of the 

 formation of more numerous and larger streams fed by the glacial abla- 

 tion and rains and carrying much sand and waterworn gravel. 



