ABSTEACTS OF PAPERS 129 



A stratigraphic papei\ gi^'ing a detailed classification and description 

 of the Niagaran rocks of northern Michigan Avas tlien read by the author 

 and brought forth discussion from Messrs. Twenhofel, Foerste, and M. Y. 

 AVilliams. 



NIAGARAN PMCKS OF THE NORTHERN PENINSULA OF MICHIGAN 

 BY G. M. EHLERS ^ 



{Ahstract) 



The Niagaran rocks of the northern peninsula of Michigan, witli the excep- 

 tion of those exposed in the Limestone Mountain outlier in Houghton County, 

 are at or near the surface of a wide belt of land bordering the northern shores 

 of Lakes Huron and Michigan. These rocks consist almost entirely of lime- 

 stones and dolomites, are remarkable for their continuity from Wisconsin to 

 Ontario, and have a maximum thickness of nearly 1,000 feet. 



A classification of these rocks is proposed in which the strata, beginning at 

 the base, are grouped under the names Mayville, Burnt Bluff, Manistique, and 

 Racine formations. 



The Mayville formation is a northeastward continuation of the Mayville 

 beds of Wisconsin. The base of the formation in Michigan has not been seen ; 

 the top is provisionally placed at the top of a yellowish gray dolomite contain- 

 ing numerous remains of the brachiopod named Yirgiana mayvUlensis by 

 Savage. This horizon extends eastward as far as Manitovilin and Fitzwilliam 

 islands, Ontario, in which regions it is included in the upper part of the 

 Cataract formation by M. Y. Williams. It is thought that this horizon is 

 younger than Cataract, and that the entire Mayville formation is of Niagaran 

 age instead of Alexandrian, as stated by Savage. The Yirgiana mai/villensis 

 dolomite of the Mayville probably represents the same stratigraphic horizon 

 as the Yirgiana (Conrhidium) deriixsata beds of Limestone Mountain. Michi- 

 gan, of the Hudson Bay region, and of the Stonewall limestone of Manitoba. 



The overlying Burnt Bluff formation seems to be limited above by a discon- 

 formity, and with little doubt is a northeastward extension of the Byron, 

 Transition, and lower part of the Lower Coral Beds of Wisconsin. Certain 

 beds of the formation — that Is, the Fiborn limestone and upper part of the 

 Hendricks series of R. A. Smith's tentative classification — are regarded by 

 Savage and Crooks as being of Alexandrian age. The Burnt Bluff formation, 

 which includes these beds, is thought by the writer to be of Niagaran age. 

 The formation without doubt is equivalent to the Severn River limestone of 

 the Hudson Bay region and the Wabi formation of the Lake Timiskaming 

 region. 



The Manistique formation is a northeastward extension of the Upper Coral 

 Beds and the upper part of the Lower Coral Beds of Wisconsin. The well 

 known coral horizon of this formation, which also occurs in the Upper Cora! 

 Beds of Wisconsin, is represented by the Fossil Hill coral horizon of the Tjock- 

 port formation of Manitonlin Island and by a similar horizon in the Lockport 

 of the Lake Timiskaming region. 



^ Introduced by E. C. Case. 



IX — Bull. Geol. Soc. Am., Vol. 32, 1920 



