NIPISSING GBEAT LAKES. 457 



drowning of the Nipissing or two-outlet beach at Duluth and raised Lake Superior to a position 

 20 feet above Lake Huron. 



The Nipissing beach is everywhere so little above the water surfaces of the present lakes 

 that it is almost always near the present shore, and hence is easily reached. In the northeast 

 corner of Lake Superior it is 110 feet above the lake, but that shore is a high coast with steep 

 slopes, so that even there it is near the present shore. It is only in the labyrinth of islands 

 along the east side of Georgian Bay and the North Channel of Lake Huron and especially up 

 the valley of French River to Lake Nipissing and North Bay that the Nipissing beach lies any 

 distance inland. All of these northern regions are still in a wild forested state, and it is prac- 

 tically impossible to trace any of their beaches continuously. 



Excepting Coleman's observations on the high beaches, the east coast of Lake Superior, 

 between Peninsula Harbor and Sault Ste. Marie has not been explored. But Lawson and the 

 writer have observed this beach at many places on the north and northwest shores. It was 

 found also at Sault Ste. Marie, at Thessalon, at Algoma Mills on the North Channel of Lake 

 Huron, and at North Bay. 



Although these observations of the Nipissing beach on the northern shores are widely 

 scattered, some of them being separated by intervals of more than 100 miles, yet this beach is 

 so distinguished from all others by its great strength and individual characteristics that its 

 identity seems to be beyond doubt at every locality where it has been reported. From these 

 scattered observations some interesting facts have been deduced, the most important being 

 that the strength of the Nipissing beach increases very perceptibly toward the north, attaining 

 its greatest development in the most northerly part of the Lake Superior basin. This is 

 significant when it is noted that the isobase of North Bay passes only a few miles south of the 

 extreme northeast corner of Lake Superior, and that the original Nipissing beach was submerged 

 in all the region south of the isobase of North Bay by the uplift that shifted the discharge to 

 Port Huron. Along the isobase of North Bay the waves were at work not only during the 

 beach of the two-outlet stage (known as the Nipissing beach), but before that, from the very 

 beginning of the discharge eastward by North Bay. The character of the outlet channel in the 

 Mattawa Valley shows that the whole discharge passed that way for a considerable time. South 

 of the isobase of North Bay the only beach of this stage of the lakes now to be seen is that of 

 the closing two-outlet stage. North of the isobase the beach of the two-outlet stage lies below 

 the original beach of the North Bay outlet, but the isobase passes so near the northeast corner 

 that the area to the north, in which the beaches are exposed, is very small, probably too small 

 to show the relations clearly. Nevertheless, the greater strength and distinctness of the beach 

 in the region of the isobase afford substantial proof of the correctness of this interpretation. 



ALTITUDE. 



In the Michigan and Huron basins the deformed portion of the Nipissing beach appears, 

 as already stated (p. 449), to hinge on the same line as the Algonquin. South of the hinge line 

 in both basins the Nipissing beach has an altitude of 595 to 597 feet, the average being about 

 596 feet. The observed variations in altitude are entirely within the normal variations in the 

 height of a beach ridge made by the waves of a lake subject only to climatic and wind varia- 

 tions. The altitude of the Nipissing beach where measured instrumentally en the north and 

 west of the southern peninsula of Michigan is given in the following tables, to which are added 

 altitudes at North Bay, Ontario, and Sault Ste. Marie. The altitude of Lake Huron is taken as 

 581 feet. 



