Niagara Falls 



1901 for the greater gorge, the time must have been at least 3,960 



Hitchcock years. This does not account for the greater width of the mouth 

 of the gorge, which may have been either waterworn, or eroded 

 by the ice-sheet. 



The sum of the figures given above amounts to 18,918 years 

 for the present gorge, to which might be added the figure for the 

 St. David's channel — making in all 22,878 years. 



Professor Spencer's estimate of the age, including the whirl- 

 pool, but not the St. David's channel, sums up 3 1 ,000 years, to 

 which he adds a thousand years for the duration of the river 

 before the advent of the falls. Sir Charles Lyell gave the figure 

 of 36,000; Professor Warren Upham, 1 0,000, and F. B. Taylor 

 would estimate it to lie between 36,000 and 50,000. 



Principal Events in the Niagara District. 



It may be useful to summarize the various episodes in the 

 geological history of the region of Niagara, as now delineated. 

 In the not distant future, geologists may be able to give them 

 value in centuries or years. 



1 . Laying down of the crystalline Archean floor, upon which 

 Cambrian and Lower Silurian terranes were deposited in order, 

 before the dry land reached as far south as Lake Ontario. 



2. Deposition of the Upper Silurian members of the series: 

 (a) Medina clays and sands resting upon the raised Lower 

 Silurian land, and extending from Lake Ontario to some distance 

 south of the falls, (b) Clinton shale and limestone, (c) Niagara 

 shale and limestone, both formed below the ocean's surface; 

 coral reefs extensive, (d) Onondaga, or Salina, salt group. 



3. Land gradually rising and attaining a considerable altitude 

 at the close of the Paleozoic era. Subaerial denudation con- 

 tinued through later periods, during which time the basin of 

 Ontario takes shape. 



4. Age of Erigan River. Drainage of country from the 



642 



