UPTILT OF LAND AT CLOSE OF ICE AGE 341 



record, we find that it was the uptilt of the land to the northward 

 which brought the glacial lake history to an end and inaugurated 

 the present system of St. Lawrence drainage. The outlet of the 

 Nipissing Great Lakes is to-day more than a hundred feet above 

 the level of the outlet at Port Huron, where the upper lakes are 

 now discharging their waters, and this difference in level can 

 only be ascribed to an upward tilting of the land since the latest 

 of the glacial lake stages. 



The abandoned strands as they appear to-day. The traveler 

 by steamer upon the upper lakes, as he comes within view of 

 each rocky headland, may note 

 how the profile against the ho- 

 rizon is notched by a series of 

 steps or terraces (Fig. 368), 

 and if he has followed the dis- 

 cussion in previous chapters, 



he will SUSpect that these ter- FIG. 368. The notched rock headland 



races mark the now abandoned of Boyer Bluff between Green Ba y and 



,. i.,, Lake Michigan (after Goldthwait). 



shore lines which have come 



to their present position through a series of uplifts of the ground 

 accompanied by earthquake shocks. As his steamer skirts the 

 shore he may chance to note a cave within the rock cliff which 

 represents the now elevated sea-arch of an ancient shore. 



Disembarking from the steamer and traveling inland at any 

 point where the shores are high, the traveler is certain to come 

 upon still more convincing proofs of the ancient strands; perhaps 

 in a storm beach of the unmistakable " shingle," half buried though 

 it may be under dunes of newly drifted sand, or possibly at higher 

 levels the highway has been cut through a shingle barrier as 

 fresh and unmistakable as though formed upon the present shore. 

 Sometimes it is the rock cliff and terrace, at other times barrier 

 ridges of shingle, or, again, it is the sloping cliff and terrace cut 

 in the drift deposits; but of whatever sort, if studied with proper 

 regard to the topography of the district, the evidence is clear 

 and unmistakable. 



The records of uplift about Mackinac Island. Nowhere are 

 the records of the recent uplift of the lake region more easily read 

 than about Mackinac Island in the straits connecting Lake Michi- 

 gan with Lake Huron. Approaching the island by steamer from 



