400 A. C. LANE 



Medina. The Lorraine, therefore, appears to be fairly uniform in 

 thickness throughout the Lower Peninsula except at the evtreme 

 north end, where it may ha"'/e been eroded. The Cheboygan well 

 shows largely 'imestone. The line at the top is quite uncertain. I 

 may have included beds corresponding to the Indiana Richmond. 



15, 16. Richmond and Medina transition beds. — This is the period 

 of deposition of coarser matter and residual red clays formed from 

 limestone during a period of continental uplift. Ulrich^ would class 

 the Indiana Richmond with the Medina and the whole group not 

 with the Ordovician but with that above. I do not doubt that he is 

 right. There is, however, a convenience in grouping it closely with 

 the shales below, since it is often lumped together with them in oil- 

 well drillings. If formed in a period of continental uplift we need not 

 expect to find it spread so far onto the continental shield. Except 

 for a few (26) feet doubtfully assigned to the Upper Medina by 

 Holt and Winchell, it has not been recognized in outcrop, nor was 

 the characteristic red facies noted in the Pickford well. At Limestone 

 Mountain the interval from Trenton to Niagara is not exposed, no 

 Medina has been found. The Cheboygan well shows that though 

 absent or nearly so along the outcrop it increases rapidly to the south, 

 since Alden and I would assign to the Medina the beds pierced by 

 that well about 142 feet of red and green shale. During this period, 

 Richmond to Medina and Clinton, there was a relatively ample supply 

 of iron to the sediments, as the Clinton ores (found in Wisconsin also) 

 show. Cummings has recently described the different horizons in 

 southern Indiana very carefully^ and agrees with Ulrich that the later 

 Richmond represents the Medina, the culminating of an uplift. With 

 this, Michigan facts are entirely in harmony, though Schuchert 

 brings in a big oscillation in the Richmond for which I have not noted 

 any evidence. 



In wells of the region near Ohio, red beds at this point of the 

 column can be identified, but what is noteworthy and significant, the 

 records do not closely correspond. For instance, at Monroe 685 

 feet and at Toledo 675 feet above the Trenton is the last distinct 

 dolomite sample (Clinton ?), with red and green shales below, whereas 



1 Science (1909), 630. 



2 Thirty-second Report Indiana Survey (1907), 621, 687. 



