SURFACE GEOLOGY. 197 
falls, had it been possessed by those concerned in this en- 
terprise. 
I ventured to predict to General Warren that an old filled- 
up channel would be found passing around the Mississippi 
rapids, and his examinations have confirmed the prophecy. 
I will venture still farther, and prediet the discovery of 
buried channels of communication between Lake Superior 
and Lake Michigan — probably somewhere near and east of 
the Grand Sable— at least, between the Pictured Rocks and 
the St. Mary's River— between Lake Erie and Lake Ontario 
through Canada,— between Lake Ontario* and the Hudson 
by the valley of the Mohawk, — between Lake Michigan and 
the Mississippi, somewhere along the line I have before indi- 
cated.. I also regard it probable that a channel may be found 
connecting the upper and lower portions of the Tennessee 
River, passing around the Mussel Shoals. This locality lies 
outside of the area where the Northern Drift deposits were 
laid down to fill and conceal ancient channels, but the exca- 
vation and the filling up of the channel of the Tennessee— 
like that of the Ohio—were determined by the relative alti- 
tude of the waters of the Gulf. The channel of the Lower 
Tennessee must have been excavated when the southern por- 
tion of the Mississippi valley was higher above the Gulf level 
than now, and Professor Hilgard has shown that at a subse- 
quent period, probably during the Champlain epoch, the 
Gulf coast was depressed five hundred feet below its present 
relative level. This depression must have made the Lower 
Mississippi an arm of the sea, by which the flow of the Ohio 
AT atis 
4 WIG POOR Ł J A i 
the lake baila, tae the line of drainage was established in what is now known as Ni- 
agara River. 
Though among the most recent of the events recorded in our surface geology, this 
choice of the Niagara outlet by the lake waters was made so long ago that all the ero- 
sion of the gorge below the falls been accomplished since. The excavation of the 
basin into which the Niagara flows — the basin of e Ontario, of which Queenstown 
i 
Heights form part of the margin — belongs to an epoch long anterio; 
