504 PLEISTOCENE OF INDIANA AND MICHIGAN. 



the reentrant angle at Salamanca, N. Y., a great ice lobe, 600 miles broad at its base, which 

 may be called the Great Lakes lobe, projected 400 miles southward. In it were merged the 

 Lake Erie, Lake Huron, and Lake Michigan lobes and a number of lesser subsidiary lobes, 

 like that of Green Bay in Wisconsin and Grand River valley in eastern Ohio. The remainder 

 of the lobe, projecting south of a line joining Chicago, 111., and Mansfield, Ohio, was shaped like 

 an inverted cauliflower. East of Salamanca a broad, flat lobe reached the islands south of Cape 

 Cod and had an ill-defined apex in New Jersey just west of New York City. This may be 

 called the Hudson-Ontario lobe, for it was formed chiefly by ice diverging feathervvise from 

 the axis of the Hudson-Champlain trough and was augmented on the west by ice spreading 

 southward from the eastern part of the basin of Lake Ontario. 



The region west of the meridian of Duluth is included simply to show how the features 

 there are related to those of the Great Lake region. 1 



No shore lines are shown in the Great Lakes area except the Glenwood or highest beach 

 of Lake Chicago, the Whittlesey beach, and the correlative beach of Lake Saginaw. 



Two hinge lines are shown. The first or Whittlesey line crosses Lake Erie from Ashta- 

 bula, Ohio, through the middle of Lake St. Clair and thence bends more to the west, crossing 

 Lake Michigan west of Grand Rapids. This line is the isobase of zero for the first or earliest 

 recognized uplift recorded by the beaches. South from this line the Whittlesey and lower 

 beaches and the beaches of Lake Chicago are horizontal and give no evidence of having been 

 uplifted or tilted. But at the hinge line the Whittlesey and Glenwood beaches begin to rise 

 northward. The horizontal part of each successive beach below the Whittlesey reaches a little 

 farther north than that of its predecessor before beginning to rise, but all of them rise before 

 reaching the Algonquin hinge line. The successive positions of the hinge line are shown with 

 approximate accuracy in figure 15. 



The Algonquin hinge line is the isobase of zero for the Algonquin beach. South of this 

 line the Algonquin beach in the Lake Huron and Lake Michigan basins is horizontal, but at 

 the line the beach begins to rise northward. On the map the Algonquin hinge line is produced 

 conjecturally eastward across Lake Erie and is made to turn toward the east in harmony with 

 the 440-foot isobase of the Iroquois beach. The conjectural eastward extension of the first 

 hinge line is also bent in the same way and for the same reason, where it crosses the unglaciated 

 reentrant angle south of Salamanca. Both hinge lines are also produced conjecturally north- 

 westward to the region of glacial Lake Agassiz. The highest or Herman beach of that lake 

 rises northeastward a little, even at the extreme south end of the lake, but Todd found Lake 

 Dakota to be horizontal. The first hinge line is therefore drawn through Traverse Lake 

 parallel with the isobases for 1,090 and 1,175 feet, both of which are based on accurate 

 measurements made by Upham. 2 The Algonquin hinge line is drawn parallel with these 

 isobases and is placed where the earlier uplift is about the same in amount as it is at the 

 Algonquin hinge line on the "thumb" of Michigan. The Algonquin isobases for 700 and 

 1,015 feet are shown and the general harmony of their trend with the two hinge lines and with 

 the western part of the 440-foot isobase of the Iroquois beach is evident. All the lines run 

 west-northwest over Lakes Huron, Erie, and Ontario, bend more westerly over Lake Michigan 

 and the eastern part of Lake Superior, and return to west-northwest toward Lake Agassiz. 

 The 440-foot isobase of the Iroquois beach bends sharply east near Rochester, N. Y. 



Two isobases of the Nipissing beach are shown. This beach comes down to the level of 

 Lake Superior (600 feet above sea level) at the head of Ashland Bay and its nodal line runs 

 about N. 65° W. from this point. The hinge line of this beach is at an altitude of 596 feet in 

 the Lake Huron and Lake Michigan basins, but its place in Lake Superior has not been 

 determined. The isobase of North Bay (700 feet) is the most northerly yet determined. (See 

 p. 460.) In the basin of Lake Superior the trend of the Nipissing isobases is quite different 

 from the Algonquin. In the basins of Lakes Michigan and Huron the Nipissing beach appears 



1 The shore lines of the glacial lakes Agassiz, Souris, Dakota, and Minnesota are taken from Warren TJpham's maps in his monograph on 

 glacial Lake Agassiz (Mon. U. S. Geol. Survey, vol. 26, 1896). 

 1 Op. Cit., pp. 278-381. 



