The Second Lake Algonquin. — Taylor. 113 
irregular, local changes of more or less importance are almost 
certain to take place everywhere. With a single exception 
already pointed out, however, the attitude of the Nipissing 
plane shows the change to have been of the broader kind, af- 
fecting the whole basin as a unit. 
In considering the process of the change of outlet, it is im- 
portant to see that unless the movement which produced that 
change was extremely sudden (and there is no reason to sup- 
pose that it was), the outtlow by the new outlet must have be- 
gun before the old one was abandoned. Dr. Spencer has said 
that the outlet could not have been southward by way of the 
St. Clair river at the time of the Algonquin beach.* But if 
we consider the case from the standpoint of the Nipissing 
beach, which is more nearly horizontal, the difficulties of such 
a supposition are greatly decreased. Indeed in this case such 
a conclusion is clearly disproved by a very simple considera- 
tion. In the tilting of a basin which has two possible outlets 
on its eastern rim, the uplift being at the north, it is clear 
that the highest shore line which can possibly be nuide be- 
tween these outlets is in a plane which connects them when 
both are flowing. A change from this position either way 
would throw the whole discharge to one outlet and 
leave the other dry. It is therefore plain that the submerged 
beach off Sarnia marks the level of lake Algonquin at a time 
when the St. Clair outlet had just been fully established and 
the Nipissing outlet just abandoned. And there are no ob- 
structions in the St. Clair or Detroit rivers which preclude the 
supposition that they might have been this much lower at that 
time. That this is not mere speculation is plain when we con- 
sider that some other outlet must have become active when 
that at North Bay went dry. But there is no other outlet 
available except that at Port Huron. After this one. the onl}'' 
other which might have been available is at (Chicago. But the 
attitude of the Nipissing plane excludes that alternative ab- 
Extension of the Xipisainy Plane to Biijfalo. The cessa- 
tion of the North Bay outlet and the complete establishment 
of that at Port Huron marked the extinction of lake Algon- 
quin and the beginning of the present order of things. Since 
*0p. cit., p. IS. Also It'tltM- ill A.MKIUCAN Geoukust Un- Aiij;iisl. KSiM. 
