POST-GLACIAL LAKES IN CANADA 341 



The formation of this dam is important in the consideration of 

 the drainage of the great lakes formed in the Athabaska and 

 Peace river valleys to the west. Tyrrell does not seem to appreciate 

 the fact that for a long period the northward drainage of the 

 Athabaska Lake Valley was blocked, and that consequently the 

 waters of Hyper-Athabaska Lake must have stood high and the 

 natural outlet of these waters would, at one time at least, be by 

 way of Black Lake and the Stone River Valley; and, therefore, 

 the damming would probably have more to do with the closing of a 

 possible outlet of Hyper-Athabaska Lake than the formation of a 

 Hyper-Black Lake. As has been already suggested, the writer 

 believes this damming separated the confluent waters of Hyper- 

 Athabaska and Hyper-Black lakes, allowing the rapid drainage 

 of the smaller Hyper-Black Lake eastward, while the water still 

 remained high in Hyper-Athabaska Lake. 



PEACE RIVER VALLEY 



If one stands on the plain level above the town of Peace River, 

 an extended view both up and down the valley of the Peace is 

 available. The strikingly flat character of the plain level is appar- 

 ent, and, if one could extend his vision, he would be struck by the 

 similarity of elevation between the level on which he stands and that 

 of the high lands lying to the north and the east. The elevation 

 of the plain at Peace River is 2,250 feet above sea-level. That of 

 the Watt Mountains is about 2,700 feet, and that of the Eagle 

 Mountains is about the same. Caribou Mountain Plateau is 

 slightly higher. The summit on the twenty-ninth base line is 

 3,225 feet, and to the northward the elevations probably average 

 over 3,500 feet. Buffalo Head Hills and the Birch Hills average 

 about 2,700 feet, and the plain level at the end of steel on the 

 Alberta and Great Waterways, sixteen miles from McMurray, is 

 2,500 feet. This similarity of elevation is conspicuous, and can 

 only point to the fact that these present outlying plateaux were 

 in recent geological times connected and formed a continuous plain 

 of fairly uniform relief. 



At Peace River, the valley of the Peace is both broad and deep, 

 and yet it is evidently well filled by the river it contains. Here 



