The. Seroiitl Lake A /;/ou</iiiii. — 7V'///or. I 77 
1. Widespread marine submergence prevailing at high lev- 
els in the north, producing a strait over the Nipissing pass 25 
miles wide and oOU I'eet deep and attaining a mean hight of 
about 1,150 feet above the sea in the basin of lake Superior. 
Another strait ]iassed at the same time over lake Tamagaming 
northeastward from lake Huron, and probably two others 
opened northward from lake Sui)erior over the Hight of Land 
to Hudson bay. 
2. On the rise of the land from the marine waters, Nipissing 
strait was the last to close and hence became the outlet of lake 
Algonquin, which was brought into existence by this change. 
3. From the first, or at least from the time of the formation 
of the Nipissing beach, the level of lake Algoncjuin was very 
close to that of the St. Clair outlet, so that only a very slight 
uplift at the north shifted the outlet from North Bay to Port 
Huron, without makingany apparent break in the plane across 
the North Bay east-west axis. The sea in the Ottawa valle}'^ 
had probabl}'' fallen only a few feet below the level of the 
North Bay outlet before this change took place. 
4. It was a very gradual and simple northward ditl'erential 
elevation which shifted the outlet, and for a considerable time 
after that the areas of the four upper lakes were affected onl}^ 
by a progressive continuance of the same elevation. During 
this change the level of the lakes swung on an east-west axis 
through Port Huron. 
5. Later, the uplift at the northeast introduced an east- 
ward element of defornuition and tilted up the Nipissing 
beach of lake Algonquin, so that it now rises 1(35 feet from 
Duluth to North Bay, and its direction of greatest rise at 
Mackinac is about N. 27° E. This uplift began long after the 
abandonment of the North Bay outlet and of the whole of the 
Nipissing beach north of the Port Huron axis, and also after 
the independence of lake Superior had been attained by the 
simple northward rise. 
6. (a) The heavy and very regular beaches of Nipissing 
and later age on the south Superior shore show that the water 
in lake Superior fell away from the Nipissing stage with ex- 
treme slowness and regularity, (b) The clitl"s of the same 
shore standing partly submerged mark the level of the Sault 
beach and show that the water fell for a vertical space of 50 
