POST-NIPISSING GREAT LAKES. 465 



A beach below the Nipissing and bearing about the same relation to it as the Algoma 

 beach in the Lake Huron basin was found by the writer in 1895 at a few places on the north 

 shore of Lake Superior. 1 It was thought at the time that this beach hinged on the outlet at 

 Sault Ste. Marie and that it marked the first establishment of that outlet and its isobase as 

 the controlling or nodal line for the tilting in that basin. For this reason the beach was called 

 the Sault beach. This correlation, however, now seems somewhat uncertain, because all the 

 points where the beach was observed are on the north shore far away from Sault Ste. Marie, 

 where Mr. Leverett has since found the Algoma beach at an altitude of 620 feet, or only 20 feet 

 above the level of Lake Superior. It seems not improbable, therefore, that the shore line which 

 the writer called the Sault beach is in fact the Algoma beach extending through a narrow 

 strait into the basin of Lake Superior. If it were permissible to suppose that the sill at Sault 

 Ste. Marie has been cut down 20 feet since it first became functional, it would at first have held 

 the water at about the level of the Sault beach. The coincidence of the two beach planes would 

 then be accidental. It does not seem probable, however, that Lake Superior could have been 

 held 20 feet above its present level for any length of time by the barrier of drift at Sault Ste. 

 Marie. The present barrier is of bedrock and affords no evidence of having been perceptibly 

 lowered by the river in postglacial time. The drift that rested on the bedrock must have been 

 quickly removed, and it seems probable, therefore, that the Sault beach is in reality identical 

 with the Algoma. 



LAKE ERIE. 



At the beginning of the present lake stage Lake Erie had become an independent body 

 and had passed through four stages. At the beginning of the present stage renewed uplift of 

 northern lands had raised North Bay, closed the outlet at that place, and brought the Nipissing 

 Great Lakes to an end. This sent the whole discharge of the upper lakes back to Port Huron 

 and Lake Erie, gave Lake Erie a large-volume discharge at Buffalo, and established its fifth 

 stage (third high stage). The uplift which produced this change had little or no effect at Buffalo 

 and probably produced no drowning in the western part of the lake, for its hinge line appears to 

 have passed a little to the north of the outlet. 



Through all the changes that have affected Lake Erie since it became an independent body 

 the rock sill at Buffalo has lowered not more than 10 feet. This lowering was probably accom- 

 plished mainly during the two low stages, which lasted longer than the high stages and made more 

 effective attacks on the sill, for during the high stages the volume of water was so great that 

 the stream glided over the sill as a smooth rapids, whereas at the low stages a low cascade or 

 waterfall came into being and attacked the rock ledge more effectively. The narrow T , deep chan- 

 nel through the ledge was probably made in this way. The crest of the Fort Erie beach ridge, 

 which marks the first stage (a high stage) of Lake Erie after its separation from Lake Ontario, 

 is now 13 to 14 feet above the lake at Fort Erie, Ontario. Assuming the average height of the 

 beach ridge to have been 3 or 4 feet above the water surface and storm beaches somewhat 

 higher, it is evident that the lake level at the outlet has lowered not more than 10 feet since 

 the time of separation. 



RECENT UPLIFT AND PRESENT STABILITY OF THE LAND. 

 GENERAL EVIDENCES OF PROGRESSING OR VERT RECENT UPLIFT. 



It used to be thought that the uplifts which have deformed the old water planes of the 

 Great Lakes progressed at a substantially uniform rate and hence were distributed more or less 

 evenly throughout the whole existence of the lakes. This conclusion, however, is not justified 

 by the facts now known. Although some slight uplift took place before the time of Lake Algon- 

 quin, the great movement did not begin until a short time before the abandonment of the Kirk- 

 field outlet. Its greatest activity was during the construction of the Battlefield beaches, for 



i Notes on the abandoned beaches of the north coast of Lake Superior: Am. Geologist, vol. 20, 1897, p. 127. 

 34407°— 15 30 



