2 2 LOWER PENINSULA. 



imagine glaciers to come, ploughing up the sediments covering 

 the old surface, dredging out a part of the old ocean bed, and 

 finally leaving it filled with the water which now washes the cliffs 

 of the restored shore line, as if it never had left them. 



As we recede southward from this ancient shore line, and have 

 passed over a belt of the Potsdam sandstone, we find the Trenton 

 limestones overlapping the sand rock, and still further, belt by belt, 

 successively occur younger rock beds, which follow each other in 

 imbricated superposition. On Mackinac Island we have reached 

 a fragment of the sediments of the Helderberg belt, which resisted 

 destruction when the lakes were carved out. A description of all 

 these rock belts I have given in the geological report of 1873. 



On the northern end of the Lower Peninsula, which forms the 

 main subject of consideration in this report, we find the Helder- 

 berg group again as the lowest of the exposed rock beds, and only 

 occupying a narrow strip of the northern shore line. The imbri- 

 cated superposition of younger formations continues southward 

 to the centre of the peninsula, where we find the Helderberg group 

 overlapped by the Hamilton series ; following it are the black 

 shales of Ohio, the Waverly group, and a central disk formed by 

 the coal measures. 



These concentric arched belts of formations continue across 

 the area now occupied by the lakes, and are met again on the 

 opposite shores of Canada, Wisconsin, and Illinois. The belt of 

 the Helderberg series strikes the Canada shore south of Gode- 

 rich ; the Hamilton group and the black shales are found in 

 Bosanquet township and on Kettle Point, C. W. 



On the Wisconsin side, the Helderberg and Hamilton strata 

 barely reach the shore at a place six miles north of Milwaukee. 

 The remainder of the shore of Wisconsin and Illinois, south from 

 there, is composed of the next older rock beds of the Niagara 

 group. 



Entering on the special description of the mentioned for- 

 mations, and of their surface distribution on the Lower Penin- 

 sula, I commence with the lowest beds, with the Helderberg 

 group exposed at the northern and southeast ends of it. 



