314 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



The relation of the Dundee to the underlying Monroe formation is one of uncon- 

 formity, marked by some erosion of the uppermost Monroe. Lane^"^ says: 



At the close of the Monroe the State [Michigan] was so elevated that slight folds which 

 occurred at the same time could be planed oflf, and the underlying formation in numerous places 

 from Mackinaw to Monroe County, made into a dolomite conglomerate. * * * So far 

 as we know it remained above water during the opening stages of the Devonian Helderbergian. 

 * * * The same disturbance that cut Michigan off once more may have opened up New 

 York to the Heilderbergian, so that while the Coeymans and Port Ewen beds were forming, in 

 New York, 300 or 400 feet in all, Michigan was mainly out of water, and not until the Schoharie 

 did deposition that has been recognized by its fossils begin in Michigan. 



Grabau ^^^ first described the occurrence of the Schoharie fauna in the Dundee. 



Lane uses Traverse to designate a division of the Devonian of Michigan which 

 overlies the Dundee and underlies the Antrim. This is a more restricted use than 

 that of Grabau,"^ who employed "Traverse" to include the Dundee and Traverse 

 of Lane. 



In the restricted sense Traverse is classed by Lane "^^ as equivalent to Hamilton 

 and Marcellus, or Erian of Clarke and Schuchert's latest classification of the New 

 York section, and as the representative of the Delaware limestone of Ohio. Of it 

 he says : 



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.) 



Following Grabau, Lane divides the Traverse as follows: 



Feet. 



Chert beds; Naples goniatite fauna at top 45-50 



Petoskey limestone; Stromatopora and buff magnesian 360 



Acervularia beds; Bryozoa beds 110 



Bell shales 80 



600 



The Antrim shale is described by Lane "^° as dominantly shale, "black and 

 bituminous at the bottom, then blue, and at the top, where it passes into the Berea 

 grit, or the horizon thereof, red or interstratified with sandstones and gritty." It 

 is regarded by Lane as equivalent to the Senecan of the New York State Survey 

 classification. It may or may not include a representative of the Genesee shale, 

 according to Lane. Of the Ohio divisions it is regarded by him as the equivalent 

 of Huron, Chagrin, Cleveland, and Bedford formations. The thicknesses cited by 

 Lane from well records range from 140+ to 480 feet. 



The passage from the Devonian to the Carboniferous in Michigan is not readily 

 placed. Generally the Antrim shale has been regarded as uppermost Devonian 

 and the Berea sandstone as the base of the Carboniferous. The plane at the top of 

 the Antrim is not determinable, however, where the Berea is absent and the Antrim 

 shale is followed by the Coldwater shale, and even where the Berea is present and the 

 lithologic division can be established, the assignment of strata to Devonian or 



