6 



Utica Slate and 



in position to the matinal (Trenton) limestone and inferior to the 

 matinal (Hudson River) shales is evidently nearly upon the horizon 

 of the matinal (Utica) black slate." 



The facts to be presented will add materially to the view ad- 

 vanced by Prof. Rogers and, it is believed, will warrant our 

 including the Galena limestone in the Utica epoch. 



The Galena limestone has been very fully described in the pub- 

 lications .and reports of Professors Whitney, Hall, Chamberlain, 

 Winchell and other authors who have written on the geology of the 

 region over which it is developed and exposed to examination. It is 

 evident that the formation is more closely related to the Trenton 

 limestone than to the Hudson River formation; and this must 

 necessarily follow from its being a limestone formation succeeding 

 a limestone and thus enabling the more persistent forms of the 

 Trenton fauna to live on in the seas under conditions that var'.ed 

 comparatively little, if we contrast the change that took place, from 

 the Trenton limestone-forming seas to the turbid waters that de- 

 posited the Utica slate. That there is such a marked change in the 

 fauna of the Galena is one of the strongest proofs of the great extent 

 of the physical change which accompanied the introduction of the 

 Utica epoch. 



The most north-easterly exposure of the Galena limestone is men- 

 tioned by Prof. James Hall as occurring on the Escanaba river 

 in the upper peninsula of Michigan. He says 



"The upper layers of gray limestone having a thickness of fifteen 

 feet which rest on the Trenton limestone do not appear to be identical 

 with any portion of the Trenton limestone farther east." 



He then shows that these beds are the probable north-eastern ex- 

 tension of the Galena limestone. 



" That the lead-bearing rock is a peculiar one, holding a certain 

 place in the series and oi limited geographical extent. ****** 

 The fact of the existence of this rock, as a distinct member of the 

 series, is interesting in a geological point of view and opens the 

 question as to the completeness of the series which have been 

 studied in New York, Canada, Pennsylvania and Virginia." 



In describing the formation in Wisconsin the same author says 



" In some localities there is an abrupt passage from the blue lime- 

 stone or Trenton limestone below, but not unfrequently some thin 

 aro-illaceous and calcareo-magnesian layers constitute beds of pas- 

 sage from the lower rock. The middle portion is heavy bedded, 

 very crystalline, and free from any considerable proportion of argil- 



1 Foster and Whitney's Report of the LoM Superior Land District, Pt. 2, 

 pp. 146, 148. 1851. 

 ^ Geology of Wisconsin, i, pp. 43, 44. 1862. 



