| ate “ What Might Have Been.” 861r 
free and the northern or eastern outlet opened, the channel at 
Mackinaw was still ice-locked and no communication was there- 
fore possible from Lake Erie to Lake Michigan. The water was 
thus ponded back and could not flow over the low dam at Chicago 
because of the existence of a high ice-dam at Mackinaw. It was 
therefore compelled to rise until it was high enough to overflow 
at the next low point—the ridge of Queenston—at whatever height 
that ridge may then have stood. 
; IV: 
_ The relationship then of Buffalo and Chicago as the outlet and 
the head of lake navigation depends on a series of geological 
changes whose results are so nearly in equilibrium that at certain 
€pochs a trifle would have been sufficient to reverse them. As 
_ with some of the lakes and streams in Northern Ohio, the break- 
ing of a dam or the cutting of a ditch is enough to divert into 
the Mississippi water that previously flowed into the St. Law- 
rence, 
a Summing up the result above obtained, we find that the Niag- 
ara river would probably never have existed and that the drainage | 
of the four upper lakes would have flowed past Chicago into the ~ 
Mississippi, SR is 
(1) If the ground at Black rock had been about twenty-five — 
feet higher when the river began to flow. : 
(2) If the ridge behind Chicago had been lower by the same  _ 
amount, i 
- (3) If the Silurian escarpment at Queenston had been as high 
=- aS itis at present. 7 T 
(4) If the reélevation of the land after the ice age had been — 
more rapid. ee 
1 (5) If the ice-dam at Mackinaw had melted before that tothe _ 
: k and east of the lakes, a 3 
; -In any of these cases it is probable and in some of them it is — 
4 long series of consequent changes of other kinds would z 
Fre tabod from the reversal of the relationship belwecn these = 
‘ two cities, _ The course of the discovery and development of the — 
“ountry could hardly have taken place along the same lines, and ` 
 &reat highways of traffic and communication, especially in 
s 
