440 PLEISTOCENE OF INDIANA AND MICHIGAN. 



In the bed of Lake Huron a well-marked escarpment, now submerged and shown on the 

 charts by the 50-fathom line, runs northwest from near Kincardine. North and east of this line 

 lies the deep trough of Lake Huron; south and west of it the lake is much shallower. The 

 general movement of the ice was southwestward across Georgian Bay and the deep trough. 

 The form of the lobation which the ice assumed under the influence of the deep trough and the 

 surrounding lands seems to find normal expression in the moraines described; that is to say, 

 the moraines are disposed about as would be expected under the laws governing the movement 

 of the ice over such a surface. The Port Elgin moraine rises only a little above the Algonquin 

 beach east of Port Elgin and Southampton, and in this respect stands in about the same rela- 

 tion to the Algonquin beach as the Cheboygan moraine near Rogers, in Michigan. 



With the ice front resting on this moraine, the waters in the south part of the Lake Huron 

 basin would necessarily discharge southward at Port Huron and the lake in that relation would 

 answer perfectly to the description Early Lake Algonquin. At the next step of ice retreat, 

 however, passages were opened possibly both to the west and east, and the discharge may have 

 passed partly, though for only a very brief time, to Chicago ; almost immediately, however, the 

 whole discharge passed to Kirkfield. 



At this stage the ice barrier rested largely in the lakes and rested on land only in Canadian 

 territory. If the recession of the ice front after as before the formation of the Port Elgin mo- 

 raine was marked by a series of halts, the moraines formed must be found mainly in the country 

 east and north of Georgian Bay and north of the North Channel of Lake Huron. The writer 

 has explored along certain lines in those wild, rough regions and has observed six or seven 

 moraines that may be members of such a series, but they are all short fragments and their 

 connections and relations are not known. Ice tongues pushed southward in two or three deep 

 valleys that enter the Ottawa Valley from the north, impinging heavily against the high south 

 side and forming effectual dams for the waters west of them. 1 These mark, it is believed, the 

 last position in which the ice sheet acted as a retaining barrier for the waters of Lake Algonquin. 

 But hi the wide stretch of country between these tongues and the Port Elgin moraine there is 

 room for a number of moraines. If rhythmical halts or osciUations of the ice front occurred in 

 this interval, as they did farther south, they will ultimately afford a good basis for the measure- 

 ment of the relative duration of Lake Algonquin and of the time and rate of the uplifting move- 

 ments which deformed its shores. 



CORRELATIVES OF LAKE ALGONQUIN. 



COMPLEXITY OF RELATIONS. 



Lake Algonquin endured for a relatively long time, during the latter part of which the 

 most profound earth movements that have affected the Great Lakes region since the time of the 

 ice sheet took place. For this reason it might be expected that the correlatives of Lake Algon- 

 quin, especially in the basins of Lakes Erie and Ontario, would have somewhat complex his- 

 tories, as indeed they have. The chief correlatives of Lake Algonquin were Lake Erie and glacial 

 Lake Iroquois. Other correlatives existed in the basins of Lake St. Clair and Rouge River. 



LAKE ST. CLAIR. 



During the time of Early Lake Algonquin the waters in the basin of Lake St. Clair stood 

 8 or 10 feet lower than in the basin of Lake Huron. Along its western side a well-defined, 

 though not very strong, old shore line, which may be called the first St. Clair beach, is 595 feet 

 above sea level at all points where it has been measured. The altitude of the Algonquin beach 

 near Port Huron is 605 to 607 feet, and therefore, in strict sense, the first St. Clair beach is not 

 the early Algonquin beach but a correlative of that beach, made at a lower level in a basin con- 

 nected with Early Lake Algonquin by a river that descended 8 or 10 feet. 



1 Taylor, F. B., Notes on the Quaternary geology of the Mattawa and Ottawa valleys: Am. Geologist, vol. 18, 1896, pp. 108-120. 



