()rl<jiii ((ml ^{(jc, of fhe L<i iir(uiti((ii Lakes. — VjiIkiih. KiS) 
ORIGIN AND AGE OF THE LAURENTIAN LAKES 
AND OF NIAGARA FALLS.* 
By Warren Upham, St. Paul. Minn. 
CONTENTS. Past'. 
Prei-'lacial Condition of tlie St. Lawrence basin 16i' 
Chau^et! brinfjins on the Ice A^e I'Jl 
Recession of tiie Ice-sheet 171 
(ilacial Lake.s in the St. Lawrence ba.sin 172 
Lake Warren 172 
La K e Alsonquiu 17;i 
Lake Iroquois 173 
Beginniufj of Niagara River and its Erosion of the Gorge below the Falls 174 
Variations of the Volume of Niagara River 17-1 
The Hypothesis of tlie Nipissing and Mattawa outlet from Lakes Huron, Mich- 
igan, and Superioi' 17."i 
Duration of Niagara Falls and of the Postglacial period 176 
Fkeglacial Condition of the St, Lawhence Basin. 
During the later half of the Cretaceous period nearly all 
the region wliieh now forms Minnesota and the drainage 
basin of the Missouri river was depressed and covered by the 
sea; but the contiguous region now forming the basin of the 
St. Lawrence continued through that time as dry land, which 
has been its condition ever since the Appalachian revolution 
terminating the Paleozoic era. On the east half of the con- 
tinent the principal drainage system that carried its detritus 
west to the (!retaceous ocean is probably marked by the chain 
of great lakes frolii Ontario to Superior, the west end of 
which is close to the east border of the broad belt of Creta- 
ceous submergence. At that time, and onward through the 
greater part or all of the Tertiary era, much of this eastern 
land area appears to have been elevated at least several hun- 
dred feet above its present level, so that streams eroded the 
deep basins which are now occupied by these lakes tributary 
to the St. Lawrence, but which then probably had a continu- 
ous westward descent. The lake basins appear to be due to 
epeirogenic movements preceding and accompanying the ac- 
cumulation and departure of the ice-sheet of the Glacial 
period, deforming the old river valleys and changing them to 
lakes, as will be presently noted. 
It seems to me most likely that the watershed dividing the 
streams tributary to the Gulf of Mexico from those tributary 
to. the Atlantic ocean and the Gulf of St. Lawrence, which 
*Prosftnted htefore the Geolotfical Society of America and Section \\ 
of the American Association for the Advancement of Science^ Aufjust, 
189(;. 
