GLACIAL LAKES TAYLOR. 321 



a dam or retaining barrier for any of its waters. The drawing of the 

 whole discharge to North Bay necessarily caused the abandonment 

 of the Port Huron outlet, which had just previously been active. 

 The new lake level, with its outlet at North Bay, lay in a plane which 

 passed somewhat, though perhaps only a httle, below the outlets at 

 Port Huron and Chicago. During the later differential upliftmg 

 of the land, which occurred while the North Bay outlet alone was 

 active, the isobase passing through that outlet became a nodal line 

 upon which the water plane swung. As elevation progressed the 

 strands to the north of this line were abandoned and left dry, while 

 those south of this line were progressively submerged by the backing 

 up of the water. 



This order of changes continued until the North Bay outlet was 

 raised as high as that at Port Huron. Then both outlets became 

 active with the discharge divided between them. The beach made 

 at this two-outlet stage has been called the Nipissing beach. In a 

 strict sense, however, it is not the original Nipissing beach, made 

 when the North Bay outlet alone was active, but a transitional beach 

 made during the two-outlet stage. It might be called the Nipissing 

 transition or two-outlet beach. The original Nipissing beach may 

 be seen now only in the northeastern part of the Lake Superior Basin, 

 where a small area hes north of the North Bay isobase or nodal line. 

 This area, however, is so small and so close to the nodal line that the 

 measurements thus far made have not yet disclosed any difference in 

 the altitude of the old water plane on the two sides of the line. The- 

 oretically there should be some difference and there j)robably is, 

 though not yet worked out. South of the hne the visible beach is 

 the transition or two-outlet beach, the original beach being everywhere 

 submerged. But inasmuch as no measurable change of plane has 

 been found in crossing the nodal line the name Nipissing beach has 

 generally been apphed to the whole extent of the two-outlet strand. 



The Nipissing beach thus defined (fig. 8) has been traced with sub- 

 stantial continuity around all three of the upper lake basins and is, 

 especially in the northern part of the area, much the strongest aban- 

 doned beach of the Great Lakes region. Its plane extends with 

 almost perfect uniformity, and with no certainly discoverable warp- 

 ing, over all the northern parts of these basins. The upUft which 

 tilted this beach (fig. 9) appears to have hinged about on the same 

 line as the earher uplifts which raised the Algonquin beaches. South 

 of this hinge line the Nipissing beach is horizontal at about 15 feet 

 above present lake level. North of it the beach rises at the rate of 

 about 7 inches per mile m a direction about N. 22° E. The Nipissing 

 beach at North Bay is now about 117 feet above Lake Huron, about 70 

 feet at Sault Ste. Marie, 48 or 50 feet at Mackinac Island, and about 



