440 J. W. SPENCER ^RELATION OF NIAGARA TO GLACIAL PERIOD 



cool epoch of the Forest Glen, which may be considered a post-Illinoisan, 

 at least two glacial formations have been left in the btiried channel, which 

 below is further filled by 100, or perhaps nearer 200, feet of drift, some 

 of the deposits of which may represent a still older Glaciial epoch. There 

 seems no reasonable doubt that the ravine at Forest Glen had the same date 

 as the ravines in the fossiliferous beds east of Toronto. The origin of the 

 Whirlpool Gorge is thus shown to be older, by at least two stages, than the 

 fossiliferous beds mentioned (which are supposed by Chamberlin and 

 Leverett to be an equivalent of the post-Illinoisan interglacial period), 

 with still an underlying accumulation of 100 to 200 feet undetermined 

 bj direct observation. This lowest drift lies in a rock-bordered valley 

 which has suffered an amount of erosion enormously greater than that 

 during or since the Glacial period. From all the evidence found I can 

 therefore only conclude that this new filled trough is of preglacial origin. 

 The age of the modern Niagara Eiver is also found to be younger than 

 the glacial deposits about the western end of Lake Ontario, though not so 

 recent as the later Wisconsin accumulations in other localities. 



Having described the relationship of Niagara Eiver to the older drift 

 deposits, its relationship to the latest ice-sheet should be referred to. 

 Before the birth of the falls, the ice had receded beyond the greatest of 

 all the moraines of Ontario, which lie between Lake Ontario and Lake 

 Simcoe and between this lake and Georgian Bay, a distance of more than 

 120 miles north of Niagara Falls; so that the drainage of Lake Huron 

 then passed down the Trent Valley, as discovered by the instrumental 

 measurements of the writer in 1888, since confirmed by Gilbert and 

 Taylor, and later remeasured by Goldthwait. From the terrace north 

 of Lake Nipissing, identified by Taylor as belonging to the level of the 

 Algonquin beach, the ice-sheet had receded 230 miles or more to the north 

 of Niagara before the birth of the falls. But the Ottawa Valley farther 

 down was still blocked. The Ontario Valley was also open to at least 

 near the eastern end of the lake, so that it permitted the flow from Algon- 

 quin Lake down the Trent Valley, although the ice was not removed 

 from the Saint Lawrence Valley till some time after the birth of the falls. 

 This was the last ice-sheet, concerning which at present we only know 

 that it disappeared so long ago that there was time for the excavation of 

 the inner gorge of Niagara Eiver, extending from Lake Ontario to a point 

 inside the canyon of Niagara, since reflooded and drowned to 180 feet by 

 the subsequent northeastward tilting of the region. 



Note. — Erigan is the name given to the buried valley and canyon which formed the 

 preglacial outlet of the Erie Valley, 



