412 PLEISTOCENE OF INDIANA AND MICHIGAN. 



N. 22° E. The isobase of Kifkfield is parallel with the hinge line. The promontories near 

 Owen Sound lie roughly 30 miles down the dip of the tilted plane from the Kirkfield isobase. 

 The uplift raised the water against the shores of the promontories near Owen Sound until dis- 

 charge was established at Port Huron and Chicago. Then as the uplift continued the level of 

 the lake at Kirkfield and Owen Sound began to fall. Thus, some of the original difference of 

 level between the water plane of Early Lake Algonquin and that of the Kirkfield or second 

 stage was lost by submergence due to the tilting, increasing the difficulty of distinguishing the 

 termination of the beach of the earlier higher plane. 



EARLY LAKE ALGONQUIN. 



The existence of Early Lake Algonquin is largely a matter of inference and is based (see 

 p. 409) not on observation of its beaches or of moraines marking the position of its ice bar- 

 rier but on its outlet, as shown by the distributaries of St. Clair River over the Port Huron 

 moiaine at St. Clair, and on certain characteristics of Niagara River. No beach marking the 

 shores of this stage of the lake is known, probably for two reasons — (1) because Early Lake 

 Algonquin endured for only a relatively short time and probably did not develop a strong 

 shore line; and (2) because when the discharge returned to Port Huron and Chicago after having 

 passed eastward for a long time by way of Kirkfield, Ontario, the lake was reestablished at or only 

 very slightly below the level of Early Lake Algonquin and remained there for a relatively long 

 time, forming a strong and relatively mature shore line and completely destroying the earlier 

 beach. At any rate, nothing has been found which seems to represent the earlier lake. 



It seems certain that the retaining ice barrier of Early Lake Algonquin barely closed the 

 passages northwest to Lake Chicago and east to the basin of Lake Ontario (by way of the Trent 

 Valley in Ontario), and that soon after the lake had become settled in its basin another 

 short step of retreat opened one or both of these passages and allowed the level of the lake to 

 fall, so as to divide the overflow with Chicago if the union with that lake came first, or so as to 

 give the whole discharge to Kirkfield, if that outlet opened first. Even if the union with Lake 

 Chicago came first the change of the whole discharge to Kirkfield came very soon after. Thus 

 Early Lake Algonquin was short lived, and the Huron-Michigan stage, if it existed independ- 

 ently before the opening eastward to Kirkfield, was still shorter. 



KIRKFIELD STAGE. 



The introductory, transitional stages of Lake Algonquin were short and the greater Lake 

 Algonquin, comprising the waters of the basins of Lakes Michigan, Superior, and Huron (includ- 

 ing Georgian Bay) , was soon established with its outlet at Kirkfield, Ontario. The lake had not 

 yet attained its greatest extent, for the ice sheet still held some of the noathern part of each of 

 the lake basins, but its condition marked the beginning of the greater lake as distinguished 

 from the much smaller Early Lake Algonquin and the intervening transitional stages. The 

 farther withdrawal of the ice gradually increased the area of the lake nearly to its maximum 

 without opening any new outlet. 



Late in the progress of the retreat of the ice a great movement of land elevation began, 

 raising and closing the outlet at Kirkfield and sending the discharge back to Port Huron and 

 Chicago and bringing the Kirkfield stage of Lake Algonquin to an end. 



The outlet for the Kirkfield stage headed about a mile northeast of Kirkfield, Ontario, where 

 the outlet river passed over a sill of limestone through an extensive swamp at nearly the same 

 level into Balsam Lake and thence down Trent River and Kawartha Lakes to near Peter- 

 boro, where it built an extensive delta of gravel in a land-locked bay of the glacial Lake Iroquois. 

 Spencer named this Algonquin River. The scouring effects of the great river are well marked 

 in the intervals between the several small lakes which form a large part of Trent River. 



