GLACIAL LAKE ALGONQUIN. 411 



same in strength, general characteristics, and relations, and yet, on theoretical grounds, it 

 seems certain that it is not strictly the same beach at all places. The plane of the highest 

 beach in one lake basin in all probability is slightly different from that of the highest in another 

 lake basin and is therefore, in precise terms, a different beach made at a different time. But 

 the planes of some of the beaches related to the different early outlets were so nearly at the 

 same level that it has not yet been possible to distinguish them in the field. Besides, in the 

 later, longer-enduring stages (Kirkfield and Port Huron-Chicago), the wave work on the shores 

 was so great that the fainter, earlier beaches of Early Lake Algonquin and of the other transi- 

 tional substages were probably entirely destroyed, even though some of them, especially that 

 of Early Lake Algonquin, probably stood slightly higher. The probability of this is heightened 

 by the fact that as the overflow gradually shifted from Kirkfield to Port Huron and Chicago 

 the lake was rising on all the shores south of the isobase of Kirkfield and was consequently 

 eroding more effectively than if it had been stationary, and much more effectively than if it 

 had been falling. The area affected included all of Early Lake Algonquin, for this lake was 

 limited to the south arm of Lake Huron and to Sagmaw Bay. 



What seems to be the highest beach everywhere except at some places in the far north 

 appeal's to be a single, continuous individual throughout. Separate "highest" beaches for the 

 outlets at Port Huron and Chicago have not been found. The visible "highest" beach south 

 of the isobase of Kirkfield appeal's to be the beach of the three-outlet phase, when the over- 

 flow was shifting from Kirkfield to Port Huron and Chicago, and its great strength indicates 

 either a pause or a very slow rate of change — probably two slow changes, first a slow rising 

 and then a slow falling. Since the visible highest beach seems a unit and covers all the basins 

 to the far north, it is convenient to speak of it as the "highest" or upper beach of Lake Algon- 

 quin, although there are theoretical reasons for believing that it really stands in the place of 

 two or three beaches at slightly different levels. The original beach of the Kirkfield outlet was 

 separated from the other two by a wider vertical interval, but it is wholly submerged south of 

 the isobase of Kirkfield. 



The first or early stage of Lake Algonquin filled only the southern arm of the Lake Huron 

 basin, though it received tributaries from lakes in the Georgian Bay and Lake Simcoe basins. 

 Whether the lake of this stage united with Lake Chicago before or after the opening of the 

 Kirkfield outlet is not known. It is certain, however, that the shifting of the whole discharge 

 to Kirkfield from Port Huron (or from Port Huron and Chicago) lowered the level of those 

 parts of the lake which had previously discharged at these two outlets by 50 to 100 feet and 

 caused both of them to go dry. If the lake changes had continued in the same order, that is, 

 if the level of the waters had continued to fall by stages without any northern uplift inter- 

 vening to bring the discharge back to the southern outlets, the beach of Early Lake Algonquin 

 and the highest beach of greater Lake Algonquin, in the south half of the Lake Huron basin 

 (and perhaps in the sc*Uth half of that of Lake Michigan) would now be seen in distinctly separate 

 planes. 



The northern limit of the beach hi the higher early plane would be determined by the 

 position of the ice front at the time when the outlet at Kirkfield was first opened. The plane 

 would end at one of the promontories which project northward both east and west of Owen 

 Sound, Ontario. A similar limit for this water plane might be expected on the west side of Lake 

 Huron somewhere on the northward slope west of Alpena, and possibly also on both sides of 

 the northern part of Lake Michigan. All of the highest Algonquin beach north of this limit 

 would lie in a slightly lower plane belonging to the time of the three-outlet phase. 



These theoretical limits for the earlier highest water plane have not yet been recognized 

 in field observations, but they may be at some future time, when the country in the critical 

 areas is cleared and researches are made hi greater detail. The great uplift, however, added 

 much complexity to the relations of the beaches. In the Lake Huron basin the hinge line of 

 the Algonquin uplift runs about N. 68° W. nearly through Grand Bend, Ontario, and a mile or 

 two north of Richmondville and Standish, Mich. The uplift was differential and produced an 

 effect like tilting, the direction of most rapid rise lying at right angles to the strike, or about 



