364 EARTH FEATURES AND THEIR MEANING 



of water, and that its lower limit marks the position of the former 

 cataract when the waters from the upper lakes were transferred 

 from the " North Bay Outlet " into the present or " Port Huron 

 Outlet " and Lake Erie. As the upper limit of the Gorge of the 

 Whirlpool Rapids thus corresponds to the closing of the " North 

 Bay Outlet " and the extinction of the Nipissing Great Lakes, 

 so its lower limit doubtless corresponds to the opening of that outlet 

 and the termination of the preceding Algonquin stage ; for in the 

 stage of the Nipissing lakes the water of the upper lakes, as we 

 have learned, reached the ocean through the northern outlet. 



Mr. Frank Taylor, who has given much study to the problem 

 of Niagaran history, believes that the Middle Great Gorge, com- 

 prising the Eddy Basin and the Cove section, represents the gorge 

 drilling which occurred during the later stage of Lake Algonquin 

 after the " Trent Outlet " had been closed and the waters of the 

 upper lakes had been turned into the Erie Basin. 



Summarizing, then, the episodes of the lake and the gorge history 

 are to be correlated as follows: 



GLACIAL LAKE NIAGARA GORGE 



Early Lakes Iroquois and Algon- Drilling of the gorge from the 

 quin. Lewiston Escarpment to the Cove 



section above the Wintergreen Flats. 



Later Lakes Iroquois and Algon- Drilling of Middle Great Gorge, 

 quin with upper lakes discharging 

 into Erie basin. 



Nipissing Great Lakes with the Drilling of the narrow Gorge of 

 upper lake waters diverted from the Whirlpool Rapids. 

 Lake Erie. 



Recent St. Lawrence drainage Drilling of Upper Great Gorge to 

 since the waters of the upper lakes the present cataract, 

 were discharged into Lake Erie 

 through occupation of the Port 

 Huron Outlet. 



Time measures of the Niagara clock. In primitive civiliza- 

 tions time has sometimes been measured by the lapse necessary 

 to accomplish a certain task, such, for example, as walking the 

 distance between two points; and the natural clock of Niagara 

 has been of this type. But men possess differences in strength 

 and speed, and the same man is at some times more vigorous than 



