Niagara Falls 



1903 from the upper lake basins, sending their waters to the Niagara 

 Upham r j ver anc j f a jj s d ur i n g a H their history. 



Lakes Algonquin and Iroquois were contemporaneous, and the 

 Ontario basin inclosing Lake Iroquois was at the same time 

 uplifted toward the northeast, with inclination of its earlier shore- 

 lines, and with gradual rise of the lake on the land westward 

 because its outlet at Rome was raised much more than the western 

 part of the basin. While these two glacial lakes were under- 

 going such changes, a lobe of the mainly retreating but wavering 

 ice-sheet lingered on the highlands north of Lake Ontario; and 

 twice its moderate readvance was recorded by deposits of till 

 intercalated with the stratified beds of a lacustrine delta, in the 

 extensive section of Scarboro Heights near Toronto. The uplift 

 of the Iroquois basin, as well as that of the Algonquin basin, is 

 thus shown to have been far advanced and nearly completed 

 during the continuance of their ice barriers. 



Latest, the glacial Lake St. Lawrence, held by the final block- 

 ade of the waning ice-sheet on the St. Lawrence valley below 

 Montreal, extended into the Ontario basin with a depth of about 

 150 feet above the Thousand Islands, but with its water level 

 beneath the present surface of the west part of this lake. In like 

 manner with the earlier Lake Iroquois, the progressing northeast- 

 ward uplift caused the level of the Lake St. Lawrence and after- 

 ward of Lake Ontario to rise upon the land in the southwest 

 part of the Ontario basin. It was during these late stages of 

 the lacustrine history of this region that the deep channel of the 

 Niagara river at the mouth of its gorge was eroded, the channel 

 being subsequently partially refilled with water by the continu- 

 ance of the northeastward land elevation. The river from Lewis- 

 ton north to its mouth has a depth of 100 to 200 feet, which 

 indicates almost as much rise of this part of Lake Ontario, for 

 no high waterfall existed to erode the very deep channel there. 



But there are, as this discussion has also before noted, ample 

 reasons for distrusting the arguments and computations of Spencer 



650 



