446 Spencer — Another Episode in the History of Niagara. 



The Modern Episode. 



The last episode, or that of the present day, is characterized 

 by the waters sinking again, so that the descent of the river has 

 been increased, and now amounts to 326 feet. But this change 

 was not continuous, for the descent was 350 feet or somewhat 

 more, while the falls were receding through Johnson ridge (see 

 fig. 2), back of which there was a preglacial valley 90 feet deep, 

 that upon being reached by the falls, caused the waters to be 

 lowered to the present amount. The dissected rocky ridge 

 is 4,800 feet across before reaching the buried valley behind 

 it (at a point near the upper bridge). Here the river 

 channel has a depth of 160 feet, although above the shal- 

 low Whirlpool Rapids. Since passing this Johnson's ridge 

 the Falls, with their height as now seen, has receded a 

 further distance of 6,400 feet — thus completing a section of 

 11,200 feet during the modern episode of two stages. The 

 mean recession of the Falls is now 4|- feet a year. 



With the last increase in the descent of the river, the lowest or 

 Gilbert cascade was reestablished, of which remnants occur in 

 the rapids at Foster's flats and at the outlet of the whirlpool.* 

 The more shallow channel of the Narrows has also given rise 

 to an intermediate cascade in the form of the Whirlpool Rapids, 

 with the descent of about 60 feet. 



The Rise of the Ontario Waters. 



Further evidence of the backing of the waters in the Ontario 

 basin may be seen in the former lagoon, behind Burlington 

 heights, at the head of Lake Ontario, where the gravel beds of 

 the Iroquois Beach epoch have been eroded and subsequently 

 covered by silt. This deposit of from four to eight feet in 

 thickness was accumulated in the quiet waters of a protected 

 bay when Lake Ontario stood at about 70 feet above its present 

 level, at which height it forms a conspicuous terrace and plain. 



The Niagara Strand is well marked in the small embay- 

 ment behind the Iroquois Beach at the outlet of the Niagara 

 gorge. Farther down the river, it is well shown as a super- 

 ficial deposit of waterworn pebbles and sand at a height of 



* This interpretation of the modern nature of the canon in front of Foster's 

 flats seems apparently to escape Mr. Taylor's observation, as he quotes Prof. 

 Gilbert: "The shoals at Wintergreen flats (i. e. those at Foster's flats) and the 

 Whirlpool Rapids are correlated with the epoch wheu the discharge of the upper 

 lakes by way of the Trent and Mattawa Valleys left the Niagara River and Falls 

 too small and weak for deep excavation " (p. 80 of Mr. Taylor's paper to be cited). 

 As the modern canon past Foster's flats is all that is being excavated by the full- 

 volume of the Niagara River, the extraordinary appeal for a cause of its small- 

 ness need not have been made to this evidently modern section had the rise of 

 waters in the gorge been known, followed by the reestablishment of the Gilbert 

 Falls over the Medina sandstone, which falls in the form of the rapids are still 

 continuing. 



