112 The American Geohxji.sf. February, 1895 
would be siibniergecl. Tliese principles are very simple, and 
it is clear enough that if from an}' cause the attitude of the 
water instead of the land itself were made to change, the re- 
sults produced would be the same. Supposing the basin to 
have two low places or possible outlets on its eastern rim, the 
results of tilting would be the same as before for east-west 
changes, but very different for those in a north-south direc- 
tion. Let us suppose to begin with that the outtlow is all by 
the northern outlet and that the southern one is dry. If the 
basin were slowly tilted up at its north side the water plane 
would swing at first on an axis passing west from the north- 
ern outlet. Northern shores would be left higher and higher 
as the movement progressed and southern ones would be sub- 
merged more and more deeply. The water at the south woidd 
therefore appear to rise upon the land ; and, if the same change 
were continued, it would eventually rise to the level of the 
southern outlet. A further tilt would spill some of the water 
over the southern outlet and to that extent reduce the outflow 
by the northern one. Still another tilt, and the whole outflow 
would be shifted to the southern outlet and leave the northern 
one dry. Along with such changes as these, there might be 
others in an east-west direction. They would affect the po- 
sition of the beaches, but not the relation of the outlets 
on the eastern rim, unless these were affected by different 
amounts. 
A study of this kind reveals perfectly the larger factors in 
the history of lake Algonquin. Until the last hour of its ex- 
istence lake Algonquin f)Utflowed by the Nipissing pass. But 
progressive upward tilting at the north soon brought the St. 
(Mair outlet into activity and ultimately gave it the whole 
discharge, leaving the Nipissing outlet dry. Subsequently', a 
continuance of the same order of change, followed by a large 
eastern uplift, has carried the northern outlet up to 160 feet 
above the present level of lake Huron, and brought the water 
up to within eight or ten feet of the Chicago outlet, whereas, 
in the time of lake Algonquin, the latter outlet was more than 
100 feet above the lake. 
In the foregoing discussion the l)asin of the lakes is sup- 
posed in each case to be tilted as a whole, as though it were 
a rigid vessel uplifted at one side. But in the course of time 
