318 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1912. 



of strong uplifting, so that probably early in the movement it was 

 raised to a position higher than the outlet at Port Huron. The Kirk- 

 field outlet was then abandoned and the discharge was shifted to 

 Chicago and Port Huron. South of the isobase of Kirkfield the 

 Algonquin beach seen to-day is not the first beach made when the 

 Kirkfield outlet carried the whole discharge, but is a transition beach 

 made when two or probably three outlets were active at once. This 

 might be called the Algonquin transition or three-outlet beach. 

 But the name Algonqum beach has generally been applied to the 

 whole strand. The original Algonquin beach is now seen only in the 

 region north of the Kirkfield isobase. While the Kirkfield outlet was 

 active and carried the whole discharge, the isobase of that outlet 

 served as a nodal Ime on which the water plane swung, and the shores 

 to the north of it were left dry and those to the south of it submerged. 



The uplifting and tilting contmued in the region north of the hinge 

 line and progressed with increasmg rapidity. Since it was aban- 

 doned, the outlet at Kirkfield has been raised altogether something 

 more than 270 feet, for it now stands 295 feet above the level of 

 Georgian Bay, and Lake Huron in the meantime has been lowered 

 25 feet by the erosion of its outlet at Port Huron. Farther north 

 and northeast the movement of elevation was still greater. 



From the fact that the Kirkfield outlet appears to have carried the 

 whole discharge of the upper three lake basins and that it was uplifted 

 and abandoned rather late in the life of Lake Algonqum, the con- 

 clusion follows that while this outlet was active the Chicago and 

 Port Huron outlets were both left dry. Tliis means that during this 

 time the shores of Lake Algonquin throughout all the region south 

 of the isobase of Kirkfield stood at a level at least a little below these 

 two outlets. Hence, the upper Algonquin beach south of the isobase 

 of Kirkfield was not made during the prmcipal activity of that outlet, 

 but durmg the transition (two or possibly three outlet) stage of the 

 lake, when a considerable part of the overflow had left Kirldield and 

 gone to Chicago and Port Huron. It is therefore a transition beach. 

 Its principal makmg and the gradual lowering of the lake for 10 feet 

 or more was wliile the overflow was at both Chicago and Port Huron. 

 The character of the Algonquin beach agrees remarkably well with 

 this conception of Lake Algonqum's history. 



(3) Tlie Port Huron-CMcago stage. — When the Kirkfield outlet was 

 abandoned, it seems ])robable that the overflow went fii-st in greater 

 part to Chicago, leaving only a relatively small part to flow south at 

 Port Huron. But the Chicago outlet rested on a rock sill and held 

 firm, while that at Port Huron was deepened with relative rapidity, 

 so that by the end of Lake Algonquin the lake level had fallen 10 feet 

 and the Port Huron outlet had taken almost all the overflow away 

 from Chicago. The Niagara Gorge, which reflects in its magnitude 



