Northern Peninsula of Michigan. 63 



few hundred square yards in extent. The rock is here a 

 coarse-grained, sandy, bluff dolomite which contains a 

 few fossils among which were the following species : 



Favosites forbesi var. 



Atrypa putilla (Hall and Clarke) 



Camarotonchiat winiskensis Whiteaves 



Homosospira subcircularis ? Savage 



Spirifer sp. 



Leperditia cf. hisingeri var. fabulina Jones 



From fragments of limestone in the drift on Garden 

 Peninsula north of Van's Harbor, excellent moulds and 

 casts of Virgiana barrandei var. mayvillensis were 

 obtained. The glacial drift in this region is immediately 

 underlain by rocks of Niagaran age, and the Virgiana 

 zone was not found in place at this locality. 



On the west side of Lime Island, in St. Marys Eiver, 

 casts and molds of shells of Virgiana barrandei var. may- 

 villensis are abundant in the upper part of a ledge of 

 coarse-grained, cream-colored dolomite that corresponds 

 to the Hendricks formation farther west, and is overlain 

 by a bed of fine-grained limestone that resembles the 

 Fiborn. 



Through the kindness of Professor E. C. Case, the 

 writers have examined specimens of Virgiana barrandei 

 var. mayvillensis that were collected from Limestone 

 Mountain in the southeast part of Houghton County, 

 Michigan. There is no doubt that the zone of Virgiana 

 barrendei var. mayvillensis in the northern peninsula of 

 Michigan represents an eastward continuation of the 

 horizon of the Mayville limestone in Wisconsin. 



The senior writer has previously shown that the early 

 Silurian rocks included between the top of the Virgiana 

 zone and top of the underlying Maquoketa in Wisconsin 

 correspond in age to the Edgewood formation of Illinois 

 and Missouri. Consequently, the Hendricks dolomite 

 and probably also the Fiborn limestone in northern 

 Michigan, including all of the Silurian strata between the 

 top of the zone containing Virgiana barrandei var. may- 

 villensis and the top of the Maquoketa, and which contain 

 fossils consistent with the Edgewood, are considered the 

 time equivalents of some part of the Edgewood forma- 

 tion, and are thus much older than the Niagaran. 



