and Birth of Lake Huron. 19 



since the Algonquin episode, to about 430 feet in 300 miles, or 

 a little more. This approximation is close upon the mean rate 

 of uplift measured east of Lake Huron. Parenthetically, it 

 may be added that President Chamberlain found clays upon the 

 western side of the lake which represent a differential uplift of 

 400 feet (although they belong to an older episode), which 

 were in part involved in the earlier Pleistocene movements. 



The Algonquin water also covered most of Lake Superior, 

 probably to within a short distance of its southwestern end, as 

 that basin is so deep ; yet the waters must have been very 

 much shallowed. Indeed, the recent backing of the waters 

 towards the head .of Lake Superior is apparent in the open 

 bays behind the bars, which cut off Fond du Lac, at Duluth. 

 The area of the Algonquin Lake or Water _may be seen from 

 what has been written, to have been vastly greater than now, 

 tilling the upper lake basins, nearly to their extreme mar- 

 gins, and overflowing the land northeast of Georgian Bay, 

 as shown on the map. On Mackinac Island and adjacent por- 

 tions of the mainland, there are several shore lines lower than 

 that assigned to the Algonquin plain and of inferior impor- 

 tance. 



In the early history of the Algonquin water, there was an 

 overflow by way of Balsam Lake and the Trent valley. My 

 first impressions of the importance of this outlet' were over- 

 drawn in the preliminary communication* of observations from 

 the field, before all of the relations had been explored. At 

 first I attached as much importance to the Balsam outlet 

 of the Algonquin basin as Mr. Gilbert did to his Mohawk 

 outlet of the Iroquois basin. As both are too shallow, the 

 demands are satisfied in neither case. Only at its highest level 

 did the Algonquin Lake overflow into Balsam Lake. Even the 

 overflow was sluggish, permitting of the formation of beaches 

 about the outlet. Before Algonquin water sank to the level 

 of its lower beaches, its discharge was by a channel below 

 Balsam outlet. The occurrence of an overflow in this last direc- 

 tion, is only one of the coincidences, as in other cases, in the 

 growth of the lake. The outlet of the Algonquin Basin, by 

 way of Lake Nipissing and the Ottawa valley, was through a 

 depression, which now rises to 707 feet above tide. This trough 

 has now an absolute depression of 168 feet below the Algon- 

 quin Beach at Kirkfield. But the altitude of the beach, in the 

 region of the old Mpissing outlet, is estimated at 600-700 feel 

 above its floor. In short the outlet was a broad strait leading 

 into the Iroquois Basin, or like the modern connections be- 

 tween Lake Michigan, Lake Huron, and Georgian Bay, 

 unless the basin were closed by a dam, and that of ice. The 



*Proc. Am. Assoc. Adv. Sci., 1888, p. 19T. 



