620 NORTH AMERICAN INDEX FOSSILS. 



the "Black River" of his Minnesota section (Fucoid bed (5) and 

 Stictopora bed (4)), and the Platteville limestone of his lower 

 Beloit or zones 1-3, which by Ulrich and Winchell are classed as 

 Upper Stones River. Calvin includes them with the Galena lime- 

 stone in the Galena stage and the upper four divisions in the 

 Maquoketa stage. 



In the upper Missisippi valley (Minnesota and Wisconsin) the 

 following divisions are recognized : 



SUPERFORMATION. 



Siluric or higher beds. 



(Generally dis conformity and hiatus.) 



Upper Ordovicic. 



Wykoff beds ^Approximate correlation = 



Maquoketa shales J Upper Richmond. 



{great hiatus) 

 Galena limestone .A. c. = Trenton. 



Middle Ordovicic. 



Black River beds A. c. = Black River. 



Stones River bed ^ A. c. = Upper Chazy 



Upper St. Peter sandstone.. J (Lowville, etc.). 

 {marked hiatus) 



Lower Ordovicic. 



Lower St. Peter standstone. 1 ,, ^ ^ , 



^, , J 1 .. A. c. = Lowest Beek- 



Shakopee dolomite > 



Oneota dolomite J 



Subformation. 



Upper Cambric, Jordan sandstone. 



The Shakopee and Oneota are classed together as the Lower 

 Magnesian limestone series : The "" Stones River " and Black River 

 beds constitute the Beloit formation of Sardeson and the Platte- 

 ville limestone of Bain. 



In the Black Hills and Rocky Mountain Front Range, Ordovicic 

 strata generally occur. The Manitou limestone is the representa- 

 tive of the basal Ordovicic but is not everywhere present. As a 

 rule the section begins with rocks of Trenton age resting by overlap 



