32 The American Geolof/fst. January. 1S95 
features shown on the shores south of the straits were most of 
them described in the earlier paper on Mackinac referred to 
above, and those at Wellsburg and Sault Ste. Marie were also 
described in a previous paper,* At the maximum of submer- 
gence the ancient strait was 75 to 80 miles wide betweeji the 
beach at Root river in Canada and the mainland on the south. 
Since the publication of the first paper on Mackinac new 
measurements of the hight of its upper beaches had led me to 
suspect that I had made them a little too high. But I have 
learned that recent instrumental leveling by the military au- 
thorities makes the beach back of the parade ground 175 feet 
above the lake. This is five feet higher than I had made it, 
and substantially confirms my first measurement. The same 
authorities make the top of the big gravel ridge behind the 
village 60 feet above the lake. This is about 15 feet higher 
than the Nipissing beach near the Grand Hotel and the Mis- 
sion House, and can hardly be considered as a part of it. 
The northward rise of the highest beach from Mackinac to 
the middle Munuscong island is at the rate of a little more 
than five feet per mile, while the rise from the latter place to 
the Root river beach north of Sault Ste. Marie is a little more 
than four feet per mile. This is a good illustration of the 
value of ancient islands in disclosing terrestrial deformations 
w4iich could not be detected otherwise. 
A wider experience in the study of deltas has led me to 
suspect that my early estimate of the altitude of the highest 
beach at Traverse City was probably placed a little too high. 
The estimate of 80 feet was based on the hight of the old 
delta of Boardman river. I have not had an opportunity, 
however, to re-examine it. 
Comparison of Shore Links. 
The following is a tabular statement of the hights in feet 
of the principal shore lines within the area of the map: 
Highest Ixeacii. 
Above sea ievel. 
Root river, near SmuU Sic Marie (Lawsoii) 1,014 
Wellsburg 910+? 
Middle Munuscong island SOO 
M a c k i n ac island 785 
C *"A Reconnaissance of the Abandoned Shore Lincsof the South Coast 
of Lake Superior," American Geologist, vol. xiii, .Tune, 185)4. 
