THE GEOLOGICAL SECTION OF MICHIGAN 413 



appears to be not merely a disconformity as between the Detroit River 

 and the Sahna but an actual unconformity, so that the Detroit River 

 beds were folded before the Dundee and Traverse were laid down. 

 Such a folding is indicated by the fact that while at Alpena there is' 

 a dip of the surface beds 42 feet to the mile to the southwest this 

 does not seem to be the case for the lower beds of the Monroe. The 

 salt is as deep to the north. Again, along the St. Clair River in the De- 

 vonian there is an anticlinal near Port Huron where the oil wells are in 

 the Traverse (Hamilton). But the Monroe beds do not follow this fold 

 The salt runs more nearly on a level. Again, around Detroit in Wayne 

 and Monroe counties, Grabau has described how the Dundee of the 

 Devonian lies on various beds of the Monroe. For the present, there- 

 fore, it will be well to keep the line between Devonian and Silurian as 

 heretofore and as Grabau wishes, remembering that with the line so 

 placed, a very Devonian-appearing fauna already existed during the 

 time of the Detroit River beds, and that, as in New York, between the 

 Helderberg and the Oriskany^ there is an unconformity and a more 

 marked one prior to the Cobleskill Rondout, so it is with the Detroit 

 River series, which from a structural point of view is closely allied 

 to the Helderberg. 



At the salt shaft, and near by, the subdivisions are, according 

 to Grabau and Sherzer: 



146 

 326 



335 



373 



180 I. Lucas dolomite (with Cylindrohelium profundum) 

 (200 feet-h) with sulphur and gypsum. 



9 c. Amherstburg dolomite (with Panenka canadensis) 

 transition to Lucas — 20 feet. 



38 d. Anderdon limestone (with Idiostroma nattressi and a fauna 



like the Hamilton). 

 40 50 



47 e. Flint rock dolomite (with Syringopora cooperi). 

 50 



420 150 feet-|- 



Sylvania sandstone beneath. 



1 Report for 1901, 67, and PI. VII. 



2 See Grabau, Geology and Paleontology of the Schoharie Valley, 1 79 ; New York 

 State Museum, Bull. g2. 



