210 J. W. Spencer — Deformation of the 



Johnson"" ridge. Below this ridge, for six miles to the brow 

 of the escarpment, the Niagara River drained the Erie waters ; 

 and boats might have sailed from lake to lake. The waters in 

 the Ontario basin did not pause long at this high level, but 

 gradually sank to the Iroquois plain 300 feet below the plain 

 of Lundy beach. The Iroquois beach marks a long rest during 

 which the early Niagara cascaded only 200 feet from the upper 

 to the lower lake, and Erie formed only the lakelet as shown 

 on the map. 



Upon the dismemberment of Warren water, the Algonquin 

 basin emptied its waters, at first through a strait by way of 

 Lake Nipissing, and later by a river in the same region into 

 the Ottawa valley. There was no connection between the 

 Huron basin and the Erie until after the terrestrial deforma- 

 tion following the Iroquois episode. Then the Huron waters 

 overflowed the southern rim of its basin and emptied into the 

 youthful Lake Erie. The ontlet of the Erie basin was also 

 raised so that the plains at the head of its basin were flooded. 

 This tilting has continued until the beach in the vicinity of 

 the falls is now raised about 160 feet above its submerged ex- 

 tension near Point Pele'e. Of this amount of tilting, only 46 

 feet have contributed to the ponding back of the waters so 

 that the lake now extends to Toledo. The deformation of the 

 Lundy beach in the Niagara district amounts to 2*5 feet per 

 mile in direction N. 10°-15° E. More detailed measurements! 

 may possibly show that the warping may reach nearly 3 feet 

 per mile. The deformation of the Iroquois beach, which is 

 newer than the Lundy strand, amounts to somewhat more than 

 2 feet per mile north of the mouth of the Niagara. 



Had the falls receded past the Johnson ridge before the 

 deformation of the region had reached the present amount, 

 the Erie drainage would have been turned into the Mississippi 

 at Chicago, just as the warping has changed the direction of 

 the outlet of Lake Huron from the Ottawa to the St. Clair 

 River. This brings us to the first possible computation of the 

 rate of terrestrial deformation of the old shore of the lake 

 region. 



A rise of T feet in the level of Lake Michigan would send 

 the waters of that lake over the rocky divide to the Mississippi. 

 A rise of 16 feet in the Erie level would effect the same result ; 

 but the silt covering this rocky floor rises 3 or 5 feet higher 

 and the Johnson ridge has been raised so that the deserted 

 banks indicating the old surface of the Niagara river are now 



* Named after Sir William Johnson who took possession of the falls about 



mo. 



f Some of these measurements were barometric from adjacent known levels, 

 and consequently closer calculations were useless. 



