34 TJie American Geologist. July, i89s> 
Fcr instance, a slight tilt of the lake region from east to west 
would shift the present outlet from Buffalo to Chicago, or a tilt 
from south to north would shift if to North Bav, Ont., and the 
Ottawa river. The outlet was actually shifted in this way from 
North Bav to its present course not many thousands of years 
ago.* But on account of its peculiar situation the Ubly chan- 
nel cannot be explained by any admissible amount of tilting. 
The Saginaw and St. Clair valleys are branches of one wide 
vallev and the Ubly channel crosses the outer end of a ridge 
which only partially separates them. There is no way to ac- 
complish this by tilting the basin, except by tilting it in a man- 
ner entirely out of harmony with the observed attitude of the 
Belmore beach, and by an amount sufficient to raise the bottom 
of the south arm of lake Huron and the mouth of Saginaw bay 
higher than the head of the channel, without at the same time 
tilting the Erie basin farther south. But such a supposition 
implies an amount of differential upheaval for which the geo- 
logical structure of the region- not only furnishes no evidence, 
but positive disproof. If the channel were in hard rock the 
antiquity of its origin and the extent of subsequent changes 
might have obscured its cause. But it is in drift and is there- 
fore of very recent geological date. 
As it appears now, the channel begins in air and ends in 
air. Without a barrier to close the Erie basin it could have had 
no lands to drain, and without a similar barrier for the Saginaw 
valley it could not have stopped at Cass City, instead of flowing 
on as a river down to the valley bottom. Independently of the 
idea of the ice-sheet, the facts on the thumb point to the fol- 
lowing conclusions. A barrier must have rested on the Port 
Huron-Saginaw moraine along the north side of the Ubly 
channel and that barrier or some other must at the same time 
have extended to the east and west so as to close the Erie basin 
on the one side and the Saginaw on the other, completely 
separating the two. Otherwise, the two basins would not have 
been turned into lakes and a great river could not have flowed 
from east to west between them.f 
*"Origin of the Gorge of the Whirlpool Rapids at Niagara." Bull. 
G. S. A., vol. 9, 1897. 
fThe great outlet channels near Syracuse. N. Y.. are equally sig- 
nificant in their relation to and obvious dependence upon an ice-dam, 
and they are in some respects much more impressive objects to the 
