IIG The A)nerican Geologist. February, 1895 
jiniounts ol' deform ation. The lines are all drawn straight; 
but it is not presumed that the points of equal deformation 
are really so exactly aligned. They are, however, very nearly 
so, and inasmuch as all the measurements, except a few by 
Spencer and Lawson, were made by aneroid, it seems useless 
to attempt a more exact representation. The discrepancies 
are nowhere greater than the probable limit of error in meas- 
urement, and the limit is small in this case. For in nearly all 
places the conditions of measurement were very favorable for 
accurate results. As to the line AA, all the nodal points are 
calculated; none were determined by observation. But the 
data for the calculations, so far as relates to lakes Michigan 
and Superior, are most of them good. Those on lake Huron 
are less certain. On Saginaw ba}^ they are entirelj' conjectu- 
ral. Only this single fact bearing on the case for that bay is 
at hand from observation: I have several times crossed the 
great flats of the Saginaw valle}^, and I regard it as certain 
that the Nipissing beach does not appear on the shores about 
its southern half. Some of Lawson's lower beaches on the 
northwest Superior shore and Spencer's on the east Huron 
and Georgian bay shores agree ver}'^ closel}^ with conjectural 
extensions of the Nipissing plane to those parts. 
The direction of the isobases was determined in theiirst in- 
stance from the points of observation which lie along the line 
CC. On comparing the altitude of the Nipissing beach at all 
the different places where it was observed, and measuring 
their bights from the Huron plane, it was found that those at 
Mackinac, Gros Cap, Old Munising, Marfjuette and Houghton 
are almost exactly at the same bight, 45 feet; and further 
that, with the exception of Marquette, they are almost ex- 
NoTE. — AftiT tilt' map which accompanies this article was ready for 
the process of reduction it was discos'ered that it was not drawn true lo 
scale. The defect is in the original map from which this was traced. 
As it stands, the map makes east and west distances a little too iireat. 
but is not distorted in a north-south direction. The defect does not 
change the relation of the isobases to the places of observation, but 
slightly increases their angle with the meridian. Inasmuch as this 
paper is of a preliminary nature, based almost entirely ujHm aneroid 
measurements, and inasmuch as the map was originally intended to il- 
lustrate rallier than to demonstrate, the defect is not considered to be 
of sufficient importance to warrant the delay necessary to make a new 
map. The distances and angles are correctly stated in the text. 
