Taylor — Highest Shore Line on Mackinac Island. 213 



road-cuts and gravel-pits are common on all parts of the island, 

 but I found not a single striated pebble in any of those below 

 the 205 foot level. Below this level the loose material of the 

 island generally appears to be rounded and water-worn. The 

 sharp angular fragments which are intermingled in small 

 quantities are of the country rock and were probably freshly 

 derived from the cliffs. I found nothing resembling bowlder 

 clay below the 205 foot level, though it probably occurs in pro- 

 tected places. 



During the last season a pit was dug at the target on the 

 short range which is against the foot of Fort Holmes hill, and 

 an excavation was also made at a higher level to obtain mate- 

 rial for filling in behind a log backstop. The pit is in the 

 trough behind the 205 foot beach, and the backstop is about 

 ten feet higher on the side of the hill. A number of beauti- 

 fully striated pebbles were found which had been thrown out 

 of the pit. Almost the whole mass of material excavated for 

 the backstop consisted of Paleolithic flint chips originally 

 derived, apparently, from the chert nodules of the limestone of 

 the upper cliffs. This excavation was about four feet deep. 



Altogether, the appearance of the surface of Mackinac 

 Island seems to show that all parts of its surface, up to the 

 level of 205 feet, has been modified by wave action since the 

 deposition of the glacial drift ; but that above that level no 

 such modification has taken place. 



An examination of the mainland north and south of the 

 island shows that they, too, have been post-glacially sub- 

 merged up to certain levels. Within a radius of 20 miles no 

 land reaches an altitude of more than 160 to 170 feet. Mc- 

 Gulpin's Point on the south side of the strait, with an altitude 

 of about 110 feet, was completely submerged. So also was 

 the high ground on the north side near Pointe La Barbe, alti- 

 tude about 110 feet, and at Gros Cap farther west and a little 

 higher. On the shores of Little Traverse Bay, about 40 miles 

 southwest, a heavy shore line is found near Petoskey at an 

 altitude of about 100 feet above the lake, and a little higher at 

 Harbor Springs on the north side of the bay. At the latter 

 place the shore line appears as a great terrace, and from the 

 head of the bay it is developed westward and northward con- 

 tinuously for a distance of more than 20 miles to a point north- 

 east of Cross Tillage. At a very early day this terrace was 

 largely cleared by the red men and is said to have been almost 

 one continuous village for its whole length. 



At the time of the great post-glacial submergence the high 

 tract north of Little Traverse Bay and west of the G. R. and 

 I. Ry. was a large island, nearly round and about 15 miles in 

 diameter. On the south side of the bay the shore line ex- 



