DISGUSSIOX BY PROFESSOR CHAMBERLIN. 245 



of the ice involved, as is fully stated, the formation of a series of three 

 prominent terminal moraines, which represent either halts or readvances of 

 the ice front. The Herman beach overrides these moraines as they come 

 down into the borders of the lake basin. This clearly indicates that the 

 completion of the beach formation was subsequent to that of the moraines. 

 But jMr. U^)ham thinks that the beach was in process of formation through- 

 out the wliole period occupied by the successive formation of the several 

 moraines and the intervening retreats of the ice. The descriptions of the 

 beach, however, clearly indicate that it is not very massive and is unac- 

 companied by any very considerable erosion. It furthermore ajipears that 

 .the southern portion is not very notably stronger than the northern portion, 

 and there is little inherent evidence that it is notably older. The natural, 

 if not necessary, inference from these facts, under the hypothesis of Mr. 

 Upham, is that the period occupied by the retreat of the ice and the fomia- 

 tion of the moraines was short, and his inferences with reference to the 

 mode of the formation of the moraines take forms in harmony with this 

 conviction. These interpretations embrace some of the most radical phases 

 of glacial action, and hence the correctness of the conception that the rather 

 slender Herman beach represents the whole time occupied by the forma- 

 tion of the several moraines and the intervening- retreats of the ice front 

 becomes a subject of the liighest importance. 



The present writer ventures to suggest that the whole history of Lake 

 Agassiz may not have fallen within the period of stationary or rising crustal 

 movement, but that the early part of it may have taken place dm-ing the 

 latter portion of the period within which the crust was being depressed. 

 There is no difference of view respecting the former higher elevation of the 

 crust and a following depression, which was in turn followed by an eleva- 

 tion. The only question is whether the history of Lake Agassiz fell wholly 

 within the stationary and rising stages, or partly within the falling stage. 

 If the early part of the lake's history occurred while the crust was sinking, 

 the lake Avould be constantly expanding its borders, and hence its beach- 

 lines would be progressively buried by the advancing waters. In this 

 way it may be supjjosed that shore-lines contemporaneous with the several 

 moraines and Avith the stages represented by the inter-morainic till sheets 



