ALGONQUIN ISOBASES 231 



the stage marked bj the Algonquin beach (see figure 2). It lasted prob- 

 ably but a short time, for as the canting of the region proceeded the dis- 

 charge was shifted entirely into the Saint Clair Eiver, while the Trent 

 Yalley and surrounding shores of the lake emerged from the water. Thus 

 a beach which had been under construction perhaps for centuries, during 

 the regime of the Algonquin Eiver and the slow rising of Lake Algon- 

 quin, was suddenly abandoned as the water-plane adjusted itself to the 

 new outlet. The canting of the abandoned water-plane progressed until 

 the beach at Kirkfield had been lifted 275 feet higher than it had stood 

 during the two-outlet stage. ^ 



Today the Algonquin beach can be followed somewhat continuously 

 from the old outlet at the head of the Saint Clair Eiver, where it stands 

 607 feet above sealevel/ to the head of the more northerly outlet at Kirk- 

 field, where its altitude is 883 feet. From here down the Trent Valley 

 the course of the ancient Algonquin Eiver is marked by a chain of extinct 

 lakes and rapids which terminated in the contemporary waters of the 

 Lake Ontario basin.^ 



ISOBASES OF TEE UPWARPED PORTION OF THE ALGONQUIN PLANE 



On the isobase map (plate 5) about 100 localities where the altitude 

 of the Algonquin 1)each has been accurately determined are shown by 

 round dots. In about 60 of these cases the measurements themselves are 

 indicated in feet above sealevel. They are as follows : 



Locality Altitude, Authority 



feet 

 West side of Lake Michigan: 



Burnt Bluff 723 W. H. Hobbs, Michigan Geological Survey, 



1907. 

 Deaths Door 660 J. W. Goldthwait, Wisconsin Geological 



and Natural History Survey, 1905. 



Rowleys Bay...- 654 Ditto. 



Oconto 620 Ditto. 



Sturgeon Bay ... 621 Ditto. 



Cormier 611 Ditto. 



Algoma 610 Ditto. 



Two Rivers 607 Ditto. 



Evanston 605 J. W. Goldthwait, 1906. 



Rogers Park 604 Ditto. 



^ This sequence of events was first recognized by J. W. Spencer, loc. cit. It has been 

 confirmed by observations of Gilbert and Taylor. 



" Since Saint Clair River became the sole line of discharge of the lake, it has been 

 deepened enough to lower the level of the waters in the Huron basin from 607 feet to 

 581 feet above sealevel. 



8 Gilbert: The Algonquin liiver (Abstract). American Geologist, vol. 18. 1896, p. 231. 



