278 Canadian Record of Science. 
the subaqueous ridge, between the Georgian Bay and Lake 
Huron, and those which are immediately beneath the 
escarpment of the Bruce peninsula, would seem to indicate 
that the waters of this bay have been at much lower levels 
than now to admit of the denuding action of waves and 
atmosphere on these subaqueous cliffs, and further, as 
already mentioned, that these cliffs formed the western 
boundary of a large and rapidly flowing pre-glacial river 
which, before the upheaval of the ridge between the Georgian 
Bay and Lake Ontario, connected these two basins, the 
denuding of the escarpment being due largely to it. 
Without further here discussing the question of a connec- 
tion between this bay and Lake Ontario, this fact is clear 
that at a period comparatively recent, and yet so far dis- 
tant that the mammoth (Huclephas Jacksoni) then living, 
has since become extinct, the Niagara escarpment formed 
the western and southern boundary of a large interior fresh- 
water sea. The terraces and ridges around Lake Ontario 
show that this basin was considerably depressed or its out- 
let blocked, or that both causes intervened, raising the 
water to levels probably more than 400 feet higher than 
now. ‘These terraces and ridges are found resting against 
the Niagara escarpment at Hamilton and Dundas, rising, 
Logan says, to a height of 318 feet, but they must in some 
cases be much higher there, as they nearly reach the sum- 
mit of the escarpment along the line of the Grand Trunk 
railway ; and whilst Bayfield mentions heights of 460 feet, 
Spencer gives the highest point on the summit near Ham- 
ilton as 516 feet. To the northward of Lake Ontario there 
are ridges of clay, sand or gravel, reaching varying heights. 
The summit on the Northern railway is attained at 755 feet 
above the lake, at twenty-six miles north from Toronto,’ but 
the levels after falling nearly 300 feet, rise again at fifty- 
seven miles to 641 feet, passing first through a gravel ridge 
at fifty-three miles. Again, on the Toronto and Nipissing 
railway, the summit station is reached at 893 feet, at 
1 Spencer’s Elevations in Canada. 
