442 Spencer — Another Episode in the History of Niagara. 



recorded some change in the history of the river, the writer 

 set to work to enquire why the channel appeared to be scarcely 

 more than about 35 feet deep, while above it, nearer the Falls, 

 its depth reaches to from 160 to 189 feet. This investigation 

 has led to the discovery of an important episode in the history 

 of the Falls, namely, that after the river reached its maximum 

 descent of 420 feet, the surface of Lake Ontario was gradually 

 raised 75 feet above the present level, and the waters stood in 

 the Niagara gorge so as to reduce the descent of the river to 

 250 feet, before the final lowering of the Ontario waters to a 

 level of 326 feet beneath those of Lake Erie. This discovery 

 will be found to explain the greater shallowness of the channel 

 at the Whirlpool Rapids than below or above. 



Revision of the Episodes of Niagara River. 



As previously described,* the first episode of the river was 

 characterized by a cascade comparable in size to the American 

 Falls, draining the Erie basin alone (whose discharge is only 

 between one-fourth and one-sixthf that of the basins of the 

 four upper lakes), and descending 200 feet into the lower lake, 

 then at the level of the Iroquois beach. This condition pre- 

 vailed until the cataract had receded about 9,000 feetj from 

 the mouth of the gorge§ (see figure 1). 



The commencement of the second episode was marked by 

 the increase in the volume of the water, owing to the drainage 

 of all the upper lakes being turned into the Niagara. This 

 caused the river to broaden its channel so that the canon, along 

 the section of Foster's flats (F, fig. 1) and for some distance 

 above, is much wider than below. But the height of the Falls 

 was not increased until after they had receded a further dis- 

 tance of 6,300 feet,|| when Foster's flats had been passed. 

 That the height was not increased is shown 'by the fact that 

 the flats represent the floor of the channel at that time, 



* See Duration of Niagara Falls. 



f The discharge was measured by the Corps of Engineers, TJ. S. A. Report 

 for 1869, p. 582. In the early part of the season, when the summer drainage was 

 coming from the upper lakes, the discharge of the Erie basin was 163 per cent 

 that of all the four lakes. Later in the season the discharge of Erie increased to 

 28-9 per cent. The mean discharge was 22-5 per cent. Consequently it would 

 be better to accept this proportion in place of approximately one-fourth. 



X Originally taken to the foot of Foster's flats, 11,000 feet; but now to only 

 where the gorge widens, near the Catholic College, for it appears that the lower 

 part of the flats have been denuded away. 



§ This section of the modern river has reoccupied the extension of the buried 

 shallow preglacial depression or valley of Bloody Run, and this in part explains 

 the change of course and the narrowness of this lower section. 



| The best development of Foster's flats is 3,000 feet long, which measure- 

 ment was originally used, but the full length is about 3,700 feet, to which length 

 is now added a section of 2,600 feet of the canon below, with a corresponding 

 breadth. 



