118 The American Geologist. February, 1895 
one foot per mile. In this case it must be assumed that 
the plane actually changes its attitude in that direction. The 
distances between the isobases, and the rise in feet from each 
to the next, are presented below in tabular form. 
Intervals. Miles Distance. Feet Rise. 
AA to HH 4.3 2.') 
BB " CC :}() 20 
CC " 1)1) 45 ^ 25 
DD " EE 95 * !)0 
AA '^ DD 120 70 
AA •' EE 221 1()0 
The apparent discrepance from a true plane between AA 
and DD are all entirely within the limit of error. There is no 
reason to infer, for instance, that the 25 feet in 45 miles from 
CO to DD represents a real increase in the rate of rise. Prof. 
Lawson's levelling makes the beach at Sault Ste. Marie 49 feet 
above lake Superior, while that at Mackinac may be a little 
more than 45 feet above lake Huron, in which case the appar- 
ent extra rise would vanish. It is a fortunate circumstance that 
three of the best points of observation, viz. : Sault Ste. Marie, 
Mackinac, and Petoskey, are almost exactly on LM, the line 
of maximum rise of the main plane. Even after allowing lib- 
erally for such deviations as appear to be present, the fact 
still remains that the most remarkable feature of the Nipis- 
sing plane is its very close approach to uniformity over an 
extent of more than 700 miles or from Duluth to Buffalo. 
Following is a table of the altitudes of theNipissing beach at 
the principal points of observation, all measured in feet from 
the Huron plane : 
Pie Island ( Lawsoii ) 64 ? 
North end Portage lake canal 50 
Houghton 45 
Eagle Harbor 00 
Lac la Belle 60 
L'Anse ;}" 
Marquette 45 
Old Munising 45 
Sault Ste. Marie 70 
Mackinac and Gros Cap 45 
Fayette and Oladstone 20 
Petoskey 25 
Worth ington, Ont., appro.x 130 
North Bay 160 
Midland 50 
