HISTORICAL REVIEW OF THE GEOLOGY OP MICHIGAN. 193 



has been obtained. It proves to belong to the Pottsville formation, 

 formerly known as the Millstone Grit, the oldest in which workable beds 

 occur. 



The development of the Portland Cement Industry has recently spread 

 to Michigan, and while drawn here first by deposits of marl, one of our 

 surface deposits to be treated by another, I think it will be found that 

 the State possesses limestones and shales which will be of great value 

 to her in this connection. 



In conclusion, as I have already given a brief summary of the forma- 

 tions below the Cambrian, I may give the rest of the geological column 

 beginning with the Bay City Well and continuing with a new well at 

 Port Huron, then taking up the Cheboygan Well, and then some of the 

 wells along the Lake Michigan shore of the Upper Peninsula. 



Coal Measures 380 plus 



Parma Sandstone 50 



Upper Grand Rapids 80 " 



Lower Grand Rapids or Michigan 220 



Upper Marshall or Napoleon 130 



Lower Marshall 320 



Coldwater Shales 760 



Berea Shales 40 



Berea Grit 170 



2,150 



END OF CARBONIFEROUS AND BEGINNING OF DEVONIAN. 



Antrim Black Shales 320 



Traverse Group (on St. Clair River) 296 



Dundee Limestone 129 



745 



END OF DEVONIAN AND BEGINNING OF SILURIAN. 



Monroe beds, above salt formation 765 



Monroe beds with dolomite, salt, anhydrite 805 



Guelph and Lockport (Niagara) dolomites 600 



Rochester Shale 70 



Clinton 60 



Medina 142 



Lorraine and Utica about 500 



Trenton 300 



3,242 



6,137 



Calciferous has not been separated. 



END OF SILURIAN BEGINNING OF CAMBRIAN. 



The Lake Superior Sandstone has been bored at Grand Marais and at 

 Lake Linden for over 1,000 feet with no important change. 

 25 



