CUTTING NIAGARAS GORGE 



ended the independence of Lake Chicago, uniting; it across 

 northern Miclii^an witli the early Lake Algonquin. Llowever, 

 as the two lakes were at the same level, it is probable that for 

 a time both the Chicago and the Syracuse outlets were used. 



Niagara River and i hi Birth of the Falls; Beginning 

 oi Independent Lake Erie 



At this period in the Lake drama Niagara River comes on 

 the stage to play an important part. When the ice of the 

 Ontario lobe withdrew far enough north so that the melt 

 waters fell below the level of the Niagaran escarpment, the 

 overflow from lakes Erie and Tonawanda fell over the rocky 

 ledge near Lewiston, New York; then Niagara Falls was born, 

 and Lake Erie became independent. No longer fed by glacial 

 streams, Erie waters became warm and gradually became 

 populated with fresh-water fish. At first the water descended 

 in a great cascade, but in a short time a pool. Cataract Basin 

 (Figure 12), was scoured at the base of the cascade, and un- 

 dercutting of the limestone ledge followed. Four other spill- 

 ways northward from Lake Tonawanda were in use, but the 

 spillway at Lewiston was the largest, and as it also received 

 the overflow from Lake Erie it could cut faster. In time it 

 drained Lake Tonawanda westward and caused the abandon- 

 ment of the spillways at Holly, Medina, Gasport and Lock- 

 port, New York, leaving them as short gorges in the escarp- 

 ment carrying small streams with cascades. Lake Tonawanda 

 was drained, until now all that is left of it is the broad part 

 of Niagara River above Goat Island. 



During the life of early Lake Algonquin, about 2,000 

 feet of the Niagara gorge was cut back from the escarpment. 

 This section is known as the Lewiston Branch Gorge. Or- 

 dinarily a stream flowing from a lake has no cutting tools 

 with which to deepen its channel, for rock debris carried into 

 the lake is left on the bottom, and the outlet stream flows 

 clear. Niagara River has always carried clear water, but it 



55 



