15 



of the Eddy basin (excluding the whirlpool). This is about 

 two miles (3-2 km.) long. Then comes the narrow, 

 shallow section of the gorge of the Whirlpool rapids, 

 three fourths of a mile (1 -2 km.) long, and finally the wide 

 deep section which the falls are now making, two and 

 one fourth miles (3-6 km.) long. Knowing the uniformity 

 of the geological structure, these variations of width and 

 depth suggested to Mr. Gilbert many years ago the possi- 

 bility of a variation of volume as the cause. The truth 

 of this interpretation could hardly be fully established 

 from a study of the gorge characters alone, but it might 

 be expected that either strong corroboration or disproof 

 of it would be found in the history of the four Great Lakes 

 which now discharge their surplus waters through Niagara 

 river. A brief statement of that part of the Great Lakes 

 history which is related to Niagara river will show how 

 many and how great have been the variations of its volume 

 and the order of their occurrence. 



OUTLINE OF THE GREAT LAKES HISTORY 

 SINCE THE BEGINNING OF 

 NIAGARA FALLS. 



THE SUCCESSION OF THE GREAT LAKES. 



Since Niagara falls first began, the great lakes have 

 passed through five stages of change. Each of these 

 stages had a different outlet from that of the stages imme- 

 diately preceding and following it, and the volume of water 

 discharged through Niagara river changed with each 

 change of outlet. The five lake stages were as follows : 



1. Early Lake Algonquin. 



2. Lake Algonquin, Kirkfield stage. 



3. Lake Algonquin, Port Huron stage. 



4. The Nipissing Great Lakes. 



5. The Present Great Lakes. 



Four of the great lakes, including lakes Superior, 

 Michigan, Huron and Erie, lie above N^ara and dis- 

 charge their waters through it at the present time. But 



