J^^ Tne American Geologist. Scptonber, 1896 
tliough it was gTadually retreating: aiul in hotli these great 
lake basins the uplift was nearly or (juite completed during 
the existence of the glacial lakes. Finally lake Algonquin, 
by the northeastward land elevation, became divided into its 
successors, lakes Huron, Michigan, and Superior. 
Lakes Algonquin and Iroquois were contemporaneous, and 
the Ontario basin enclosing lake Iroquois was at the same 
time uplifted toward the northeast, with inclination of its 
earlier shore lines, and with gradual rise oi' the lake surface 
westward because its outlet, at Rome, was raised much more 
than the western part of the basin. Wiiile these two glacial 
lakes were undergoing such changes, a lol)e of the mainly re- 
treating but wavering ice-sheet lingered on tiie 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 continu- 
ance of their ice barriers ; and also thus it is demonstrated 
either that no outflow from .Georgian ba}' and the upj^er lakes 
ever passed to the Mattawa, or that it was of very short dura- 
tion. The whole time of existence of lake Agassiz, as esti- 
mated by comparison of its shore erosion and beach accumu- 
lation with tiiose of lake Michigan and others of the 
Laurentian lakes since the departure of the ice-sheet, appears 
to have been about 1,000 years. In comparison with this, we 
may confidently assert that, if any outflow passed for a time 
over lake Nipissing to the Mattawa river, it could have done 
so only for a few decades of years. 
Duration of Niagara Falls and ok the Postglacial 
PERIOD. 
About three-fourths of the ])eriod of 82,000 years whicli 
Spencer assigns as the age of the Niagara river and falls are 
tlerived from this hypothesis of the Mattawa outlet from the 
upper lakes, which, as I believe, is untenable, or at the most 
had only a very short existence. Leaving out that element of 
the problem as insignificant, and dividing the length of the 
Niagara gorge (about six and a half miles) by the recent rate 
