214 Taylor — Highest Shore Jbine on Mackinac Island. 



tends inland eastward from Petoskey at least 20 miles, and 

 passes south of Crooked, Pickerel, Burt and Mullet Lakes. 

 Beyond this its place is not yet determined. Southwest from 

 Petoskey the old shore line is quite irregular but continuous, 

 at least as far as Traverse City, a distance of about 50 miles, at 

 which point the old delta of the Board man River shows the 

 water level to have been at an altitude of about 80 feet. 



The identity of this great deserted shore liue with that 

 found on the shores of Lake Huron and Georgian Bay, called 

 by Professor J. W. Spencer, the Algonquin beach, and de- 

 scribed by him in recent numbers of this Journal, seems almost 

 certain. The upper beaches of Mackinac Island are without 

 doubt only an isolated part of the same great shore line. 



It is well known that almost the whole of the northern 

 peninsula of Michigan has been submerged since the glacial 

 epoch. This area of submergence is continuous with that 

 which I have described on the south side of Mackinac Strait, 

 and includes a large part of the south shore of Lake Superior. 

 Some years ago I saw deserted shore lines near Au Train, at 

 Marquette and at the west end of Lake Superior which prob- 

 ably belong to some stage of the same epoch of submergence. 



The old shore . line between Traverse City and Mackinac 

 Island shows the same northward rise as has been found in 

 post-glacial shore lines elsewhere. From Petoskey to Mack- 

 inac Island the northward component of distance is about 33 

 miles and the Mackinac beach is about 100 feet higher than 

 that at Petoskey. The northward component of differential 

 elevation between these points is, therefore, three feet per 

 mile. From Traverse City to Petoskey the northward com- 

 ponent of distance is about 41 miles, and the difference of 

 elevation of the beaches is approximately 20 feet, making the 

 northward factor of differential elevation six inches per mile. 

 Two isolated observations near Levering and Pellston 15 miles 

 north of Petoskey on the G. P. and I. Py. seem to show an 

 elevation for the shore lines at those places of not less than 

 150 or 160 feet. This is somewhat higher than the plane 

 directly connecting Petoskey and Mackinac Island. But the 

 local variation of differential elevation which seems to be sug- 

 gested by these two observations needs further verification. 



Near Harbor Springs and Wequetonsing on the north side 

 of Little Traverse Bay, and at Petoskey and Traverse City, 

 the evidence that post-glacial submergence has not extended 

 above the level of the observed old shore line is fully as plain 

 as on the island of Mackinac. This statement applies to the 

 surface forms and the composition of the drift, and also to the 

 presence o^ striated bowlders in the drift above the line and 

 their absence below it. Back of Petoskey the hills rise 300 



