STUDIES OF SPECIAL LACUSTKAL HISTORY. 105 



One of tlie most interesting discoveiies in connection with the beaches 

 of Lake Agassiz, is that they are no hMiger lioiizontal. and l)esides do not 

 lie in phiins that are parallel one Avith another. The highest water line 

 when followed northward has been found to rise at the rate of 200 feet in 

 300 miles. There are five beaches that are especially j^rominent and 

 mark a lingering of the lake surface at their respective horizons. The 

 hiohest of the series, known as the Herman l)each, when traced nortliward 

 from the southern end of the Red River valley, has l)een found to dnide 

 into several beaches at different levels ; the vertical intervals between the 

 division increasing northward. The meaning of this fact seems to be that 

 the land was rising at the north at the time the beaches were formed and 

 at the same time the surface of the lake Avas lowered by reason of the 

 opening of new outlets. 



To the north of Lake Winnepeg the higher of the ancient beaches are 

 absent and the lower ones difficult to trace. The country still farther 

 toward Hudson bay is low and does not present a barrier that under any 

 plausible hypothesis could have been made to act as a dam to retain the 

 waters of Lake Agassiz. AVhat then could for a time have reversed the 

 drainaore and led to the formation of a lake over a hundred thousand 

 square miles in area ? 



Tlie origin of Lake Agassiz as explained by Upham, is in harmony 

 with the history of the former lakes of the Laurentian basin. It is sup- 

 posed to have owed its origin to the presence of a vast ice sheet over the 

 Hudson bay region which dammed the northward drainage of the Winne- 

 peg basin and caused the waters to rise until an outlet Avas found at the 

 south and River Warren began to floAv. When the ice retreated, ncAV 

 outlets at loAver levels became aA'ailable at the north and the Avaters fell, 

 but linpfered for a time at the horizon of each of the various beaches that 

 have been referred to, at lower levels than the Herman beach. 



There are facts in connection Avith the ancient floods of the Laurentian 

 and Winnepeg basins, Avhich seem to indicate that the Aveight of the iw 

 during the Glacial epoch caused the land to subside, and that when the 

 ice melted an upAvard movement Avas initiated. These movements, and 

 also the attraction of the ice body to the north of Lake Agassiz, have 

 been thought to explain tlie gradual rise of the beaches Avhen traced 

 nortliAvard. 



The stranjje transformation that tlic Wiiiiu'i)('i>- Itasiii underwent in 

 Pleistocene times, leads one to Avondcr if in the region now drainiMl by 

 Mackenzie riA'er. and occupied in ])art by (>i'i'at Slave and (iieat IJear 



