41 6 A. C. LANE 



typical Schoharie fauna, agreeing with Hall's determinations on 

 Mackinac Island 50 years earlier. We must then grant the occurrence 

 of magnesian beds near the base of the Dundee. It would be 

 strange if overlaying a magnesian formation the base were not mag- 

 nesian. The paleontological and structural dividing line may be 

 a few feet beneath the lithologic line which I have had to use. 



26. Traverse (Hamilton and Marcellus, Erian of Clarke and 

 Schuchert, Delaware' of Ohio). 600 feet. — As this group is much 

 thicker and better exposed in the north end of the state and its very 

 existence along the south line of the state has been doubted, we begin 

 our description from the north where it outcrops on Grand and Little 

 Traverse Bays, and thence is frequently exposed around to Alpena 

 and Thunder Bay, and is nearly uniform in thickness (600 feet with 

 a basal shale. Bell shale, 80 feet, which corresponds to the Marcellus 

 and is persistent throughout the state). 



Grabau gives: 



Chert beds 45^5° Naples goniatite fauna at top 



Petoskey limestone 360 Stromatopora and buff magnesian 



Acervularia beds no Bryozoa beds 



Bell shales 80 



600 



When we get to Port Huron, nearer the Cincinnati arch, it seems 

 to have shrunk to 330 feet or so. Thence down to the Ohio line 

 it tends to shrink especially toward the axis of the arch. But the 

 marked black or blue shale base persists. Hence there is reason to 

 suspect that the loss is mainly by removal of the top. This would 

 imply that our early Traverse is Schuchert's late Hamilton, Plate 

 76. There is a fairly persistent division to which the drillers apply 

 customary names. 



Cooper's 2. Petoskey limestone. The "top lime" 85 ± (sometimes pyritic at 



its top). 

 Cooper's 3. The "top soap rock" 150 ±. 

 Acervularia beds. "Middle Hme" 4-15. Never thick, but persistent, the 



Encrinal limestone ? 

 Bell shales? "Bottom soap rock" 65. Darker than the other. 



I Sandusky has been discarded. 



