332 PLEISTOCENE OF INDIANA AND MICHIGAN. 



Except in the basin of Lake Superior, the uplift which afterward tilted this beach appears to 

 have hinged about on the same line as the earlier uplifts which raised the Algonquin beaches; 

 in the Lake Superior basin it lies some distance north of the Algonquin hinge hue. 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 to the mile in a direction about N. 22° E. 

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

 at Sault Ste. Marie, 48 or 50 feet above at Mackinac Island, and about 130 feet above (110 feet 

 above Lake Superior) at Peninsula Harbor, near the northeast angle of Lake Superior. 



The Nipissing beach shows remarkably strong development and maturity in all the northern 

 parts of the basins, especially near the nodal line. For 150 miles or more south of the nodal 

 line it is very strong, but farther south it seems gradually to diminish in strength, until in the 

 area of horizontality it is little if any stronger than the Algonquin beach. 



At the western end of Lake Superior the Nipissing beach appears to pass a little under the 

 present lake level, a relation which probably accounts for the drowned condition of the shores 

 and stream mouths of that region. 



During the Kirkfield stage of Lake Algonquin the Port Huron outlet and St. Clair and 

 Detroit rivers were abandoned and left dry, and they were abandoned in the same way during 

 the time of the Nipissing Great Lakes. At both times Niagara River was robbed of the over- 

 flow of the upper three lakes, which amounted to 85 per cent of its volume. 1 



The Nipissing Great Lakes came to an end when the northern uplift raised North Bay 

 enough to close that outlet and shift the whole discharge back to Port Huron. With this change 

 the modern Great Lakes have their beginning. 



POST-NIPISSING GREAT LAKES. 



After the overflow came back to Port Huron the northern uplifting continued, though 

 apparently more slowly, there being a series of fainter beaches on the slope below the Nipissing 

 beach. One beach, especially, is slightly stronger than the rest and seems to mark a pause in 

 the uplifting movement. This beach is called the Algoma beach because of its development at 

 Algoma Mills, Ontario, where it lies about 50 feet above Lake Huron and 35 feet below the Nipis- 

 sing beach. The Algoma beach has been found at many places farther south in a position a 

 little more than halfway up from the present shore to the Nipissing beach. , ■ 



On the north shore of Lake Superior a beach of moderate strength, standing in about the 

 same relation below the Nipissing, was at first thought to be a beach belonging to the Lake 

 Superior basin alone and determined by the outlet of that lake at Sault Ste. Marie. It was 

 called the Sault beach 2 and was thought to swing on the isobase of that place as on a nodal 

 line. It is believed to be submerged on the south shore of Lake Superior and around the west 

 end. The Algoma beach appears to be due to a pause in the uplifting movement. In all prob- 

 ability there is a beach corresponding to the original description of the Sault beach, but it has 

 not been certainly identified. 



LAKE ERIE. 



After Lake Erie became separated from Lake Ontario it ceased to be a glacial lake and 

 from that time on was entirely independent of the ice sheet. By the time the separation had 

 been accomplished following the fall of Lake Luncly, the basin of Lake Erie had probably been 

 brought nearly to its present attitude. Since its separation it has had two low stages, while the 

 Kirkfield and North Bay outlets were active, during which it was not receiving the discharge of 

 the upper lakes. The Fort Erie beach, declining gently westward along its north shore from 

 Fort Erie, Ontario, where it is 15 feet above the lake, is, at least at its east end, the correlative of 

 the beaches of Early Lake Algonquin and of the Port Huron-Chicago stage of the greater Lake 

 Algonquin. The two low-stage beaches made in the basin of Lake Erie during the Kirkfield 

 stage of Lake Algonquin and during the Nipissing Great Lakes lay very nearly in the same 

 plane, and both are now everywhere submerged. 



i Taylor, F. B., Niagara folio (No. 190), Geol. Atlas U. S., TJ. S. Geol. Survey, 1913, pp. 21-22. 

 2 Taylor, F. B., The second Lake Algonquin: Am. Geologist, vol. 25, March, 1905, pp. 166-167. 



