GLACIAL AND POSTGLACIAL HISTORY OF GREAT LAKES REGION. 329 



this lake received a large affluent from the east, from the region of the Nottawasaga Valley 

 and Lake Simcoe hi Ontario, and also a large amount directly from the ice barrier. 1 



Kirkfield stage. — There is no reason to suppose that the Chicago outlet was at first low 

 enough to take the whole discharge from Port Huron. On the other hand, the Trent Valley 

 outlet at Kirkfield, Ontario, was surely low enough, and as soon as a way was opened to it the 

 overflow went there and the level of the lake fell below the outlets at Port Huron and Chicago, 

 for the character of the outlet channel at Kirkfield and below shows that it carried the full 

 discharge of the upper lakes for a long time. Indeed, the principal or upper strand of the 

 Algonquin group of beaches is remarkably strong and continuous not only in the southern 

 parts of the basins but runs on unbroken in the same character far toward their northern sides. 

 If it is lacking anywhere it can be only on the far northern sides of the basins, for it is strongly 

 developed on the high ground north of Sault Ste. Marie, Ontario. Apj>arently during the making 

 of the upper strand the lake was nowhere subject to deforming or warping influences and the 

 outlet was at Kirkfield. 



At length when the ice sheet had almost entirely disappeared from the lake basins a great 

 movement of differential elevation began to affect the land. This movement embraced a vastly 

 greater area than that of the Great Lakes, but within this area it affected the northern parts 

 most. South of a line running through the middle of the "thumb" of Michigan and across the 

 south arm of Lake Huron about S. 68° E. and also south of a line running westward across 

 Lake Michigan from a point south of Frankfort the Algonquin beach was not affected at all 

 by the uplift. This line was a sort of "hinge" line for the movement. Kirkfield at the head 

 of the Trent Valley outlet was well within the region of strong uplifting, so that probably early 

 in the movement it was raised to a position higher than the outlets at Port Huron and Chicago. 

 The Kirkfield outlet was then abandoned and the discharge was shifted to Port Huron and 

 Chicago. South of the isobase of Kirkfield the Algonquin beach of 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 Algonquin 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 line on which the water plane swung, the shores to 

 the north of it being left dry and those to the south of it drowned. 



In the region north of the hinge line uplifting and tilting progressed with increasing 

 rapidity. The outlet at Kirkfield was raised altogether something more than 270 feet after 

 its abandonment, 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 amount of elevation was still greater. 



Northward from the hinge line the beach for some distance rises gradually, but about on an 

 isobase passing through Traverse City it begins to rise more rapidly and begins also to split into 

 a vertically diverging series of subsidiary strands which are separated by wider and wider ver- 

 tical intervals toward the north. This splitting of the strands toward the north shows that 

 the land was being differentially elevated during the life of the lake. The different strands 

 are not of the same strength nor are they equally spaced vertically, showing apparently that 

 the uplifting movement was not steady hi its progress, but was marked by a number of longer 

 or shorter pauses. 



The split-up strands seem to fall naturally into three groups, the upper group keeping close 

 parallelism for the farthest distance north and apparently recording relatively slow movement 

 in the beginning of the uplift. They probably record also some lowering of the lake by down- 

 ward cutting at the outlet, but the amount was certainly small. In the Lake Superior basin the 



i If the plan of naming the lake stages wore strictly adhered to a separate name would be applied to this stage and the name Algonquin would 

 not be used. This stage should be put under the head of " Glacial lakes in the Huron basin." But partly because there was at first a lack of com- 

 plete proof of the existence of this stage and partly because the multiplication of names for lake stages seemed undesirable, the name Early Lake 

 Algonquin was used and it has now appeared so many times in printed texts and on published maps that it seems impracticable to make a 



