204 BULLETIN OF THE 



111 some cases, notably in the somewhat continuous kaaie belt which 

 extends up the Genesee valley from its mouth to its source, we are 

 compelled to believe that the stream flowed beneath ice which probably 

 had, at least over a part of the path followed by the current, a depth of 

 half a mile or more. It is impossible to believe that the water supply 

 of this stream could have been furnished by the descent of the fluid 

 from the surface through crevices to the bed rock, for owing to the ease 

 with which ice moves under pressure the weight of the superincumbent 

 materials would make the maintenance of such passages for the descent 

 of the waters impossible. We are therefore driven to the conclusion 

 that these subglacial channels occupied by the rivers which flowed upon 

 the bed rock were fed from the melting which occurred at the base of 

 the glacier. 



The foregoing considerations make it appear likely that the water 

 lying at the base of a continental glacier would be subjected to the very 

 great pressure of the overlying ice. With ice having a depth of three 

 thousand feet this pressure would amount to near ninety tons to the 

 square foot. 



It appears tolerably evident that, notwithstanding the pressure of 

 the superincumbent glacier, the water which flowed beneath it passed 

 through continuous arches leading from the interior portions of the ice 

 field towards its margin. We may, therefore conceive that this water, 

 for doubtless it had to wrestle with the ice for passage, moved irregu- 

 larly towards the margin of the glacier, making its way in a violent 

 manner by the obstructions which it encountered. The position of 

 the kames of serpent iform outline whicli mark the position of these 

 ancient subglacial streams clearly indicates that the course of the ice- 

 covered waters was liable to much change; as is shown by the eskers, 

 their paths shifted in a somewhat sudden manner from one side of the 

 valley to the other. Xear the margin of the ice where the depth of 

 the sheet would permit the formation of crevasses which for a time at 

 least would remain open, the erratic movements would doubtless be 

 greater in amount than in the sections where the ice was so deep as to 

 prevent the formation of fractures. We may fairly conceive that the 

 motion of these subglacial streams, urged as they were by a pressure of 

 many tons to the square foot, would, at least near the margin of the ice 

 sheet, take place with paroxysmal violence. Quantities of the debris 

 which came in the path of these vigorous currents would doubtless be 

 urged laterally away from the axis of motion of the glacier, or borne up 

 from near the bed rock into higher lying parts of the ice. Each ecu- 



