Niagara Gorge and Postglacial Tiiiic.—Uphain. 239 
of lake xA.gassiz, as soon as the land was unburdened by the 
glacial retreat. This northward uplift was in progress while 
yet the ice barrier remained farther north and northeast, hold- 
ing in succession the glacial lakes Warren and Algonquin, 
besides several earlier and smaller glacial lakes which be- 
came merged in lake A\'arren, on the upper part of the St. 
Lawrence basin. In the areas of lake Agassiz and of the 
Laurentian lakes alike, the uplift was nearly completed dur- 
ing the existence of the glacial lakes, as is known by the al- 
most undisturbed horizontality of the latest and lowest gla- 
cial lake beaches. Finally lake Algonquin, by the northeast- 
ward land elevation, became divided into its successors, lakes 
Huron, Michigan, and Superior. 
Instead of the hypothesis of long continued eastward out- 
flow from lake Algonquin, mv studies convince me that the 
Trent and Mattawa outlets were occupied successively dur- 
ing only a brief time, or, more probably, that these outlets 
were obstructed by the receding ice-front until after the land 
there had risen from its Champlain depression to such alti- 
tude that the St. Clair and Detroit rivers continued to be con- 
stantly the outlet from the upner lake basins, sending their 
waters to the Niagara river and falls during all their history. 
Lakes Algonquin and Iroquois were contemporaneous, 
and the Ontario basin inclosing lake Iroquois was at the same 
time uplifted toward the northeast, with inclination of its 
earlier shorelines, and with gradual rise of the lake on the 
land westward because its outlet at Rome, N. Y., was raised 
much more than the western part of the basin. While these 
two glacial lakes were undergoing such changes, a lobe of 
the mainly retreating but wavering ice-sheet lingered on the 
highlands north of lake Ontario ; and twice its moderate re- 
advance 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 con- 
tinuance of their ice barriers. 
Latest, the glacial lake St. Lawrence, held by the final 
blockade of the waning ice-sheet on the St. Lawrence valley 
below Montreal, extended into the lake Ontario basin with a 
