200 ROCHESTER ACADEMY OF SCIENCE. 



(7) This theory does not explain adequately or satisfactorily 

 the derivation of reticulated ridges, also the derivation of eskers 

 whose direction was transverse to the direction of ice movement, or 

 the meanders often quite symmetrical that are frequently exhibited 

 by eskers. 



(8) Esker ridges formed in this way should be banded in 

 structure. The coarse wash deposited by spring floods should be fol- 

 lowed by layers of finer material as the volume of the river dimin- 

 ished in the smnmer, thus there should result a passage from cannon 

 shot gravel through fine gravel to sand. Eskers do not show this 

 feature (44). 



(9) The constant association of eskers with terminal and 

 recessional moraines indicates their formation at a time when the 

 ice front was nearly or qviite stationary building the moraine, not at 

 a time when it was in rapid retreat. See figure 4. 



Conclusion. Of these several objections 1, 3, 4, 7. 8 and 9 are 

 the most weighty, and especially the last, 9. This one alone would 

 seem to preclude the possibility of the theory as applied to the 

 formation of the vast majority of eskers. 



Euglacial hypothesis. This hypothesis has never been seriously 

 entertained or advocated. It is subject to essentially the same 

 objections as the superglacial hypothesis, and while it is possible that 

 nearly stagnant ice may be traversed by tunnels above its base, as 

 indicated by observation (80), yet it is improbable that any deposits 

 of significance have ever accumulated in such tunnels. 



Ice canyon hypothesis. The ice canyon theory has been elab- 

 orated particularly by Upham. N. H. Winchell seems to have en- 

 tertained similar views earlier than Upham (120). 



Statement. It is maintained that superglacial melting was rapid 

 during summer but subglacial melting was slow both winter and 

 summer. During the warm season the subglacial courses were 

 inadequate for the transportation of all the water derived by abla- 

 tion, and further tended to be "obstructed and closed by the trans- 

 portation and deposition of modified drift." The melting ice border 

 then became deeply incised by superglacial streams for a distance 

 of 50 to 200 miles back from the ice edge. These numerous streams 

 had steep gradients and, corrading rapidly, soon came to flow in 



