62 NEW YORK STATE MUSEUM 



Lakes Algonquin and Iroquois were probably contemporaneous, 

 and it is believed that for a time the former discharged its waters 

 to the latter by way of Balsam lake and along the course of the 

 Trent river. This discharge by way of the Algonquin river, as this 

 old outlet of Lake Algonquin has been called, robbed the Niagara 

 river of seven eighths of its water supply, which up to then had 

 reached it by the present course through the Detroit river. As a 

 result, the volume and erosive power of the river were for a time 

 enormously diminished. (Fig. n and 13) 





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Fig. 12 Gilbert's map of the Great lakes at the time of the Nipissing outlet. Modern hydrography 

 dotted. 



During the farther retreat of the ice front, a still lower pass was 

 opened by way of Lake Nipissing and the Mattawa river into the 

 Ottawa. By the time this outlet was opened, the ice had also dis- 

 appeared from the St Lawrence valley, and the outlet of the waters 

 of the great lakes was transferred from the Rome channel to the one 

 at the Thousand islands, Lake Iroquois at the same time subsiding 

 to Lake Ontario. (Fig. 12 and 14) 



The successor of Lake Algonquin, after the change from the 

 Balsam lake to the Nipissing lake outlet, has been named by Taylor, 

 Nipissing great lakes, while the river which carried its discharge to 

 the Ottawa was called by him the Nipissing-Mattawa (fig. 14). 



