T. E. Savage — Relations of the Alexandrian Series. 35 



are always associated with the above in the normal Edgewood 

 strata makes it improbable that the sea in which the strata at 

 Winston were laid down was connected with the southern 

 Edgewood basin. For the early Silurian rocks exposed at the 

 south end of the Chicago Great Western tunnel and equivalent 

 strata in northwestern Illinois and northeastern Iowa represent- 

 ing about the same period of deposition as the Edgewood 

 formation farther south and east, but which are thought to 

 belong to a northern province, the name Winston limestone is 

 proposed, from the locality where this limestone was first 

 recognized. 



Strata corresponding to the Winston limestone as exposed at 

 the tunnel, outcrop in several places along the bluffs of Mis- 

 sissippi river in Carroll County, Illinois, and Jackson County, 

 Iowa, where they are unconformably overlain by the very 

 cherty horizon of the Hopkinton dolomite. In the northwest 

 part of Belleview, Iowa, a thickness of about 40 feet of this 

 limestone is exposed. The thickness decreases southward so 

 that less than 18 feet are present at Savanna, Illinois, and these 

 strata are seen to feather out in the river bluff between Sabula 

 and Elk Eiver, Iowa. 



The Winston limestone as here defined includes only the 

 lower part, below the cherty dolomite, of the division design- 

 ated by Wilson* as the basal member of the Niagara limestone 

 in northeastern Iowa. 



The Waucoma limestone. — Strata representing the time in- 

 terval of the Sexton Creek limestone of northeastern and 

 southern. Illinois appear to be absent in the Mississippi river 

 bluffs, but they are present in Jo Daviess County, Illinois, and 

 occur farther northwest in Iowa. The best exposures known 

 are along Little Turkey river in Eayette County, Iowa, where 

 a ledge of light gray, non-magnesian limestone 10 to 20 feet 

 thick outcrops in several places between the villages of 

 Waucoma and Auburn. This limestone rests unconformably 

 upon the Maquoketa shale, the Winston limestone being 

 absent in this region. It is succeeded by normal Hopkinton 

 dolomite of Niagaran age. An outcrop of this limestone in 

 the banks of the river three miles southeast of Waucoma 

 furnished the following fossils : Clathrodictyon vesiculosum 

 Diphyphyllum cf. ccespitosum, Pachydictya sp., Atryjpa 

 cf. marginalise Dinooolus sp. (The same species is found 

 in the Sexton Creek limestone, having the shell less 

 circular in outline, and the interior platform narrower in pro- 

 portion to the length than in D. conradi.) Zeptmia rhom- 

 boidalis, Platystrojphia daytonensis, Plectambonites transver- 

 salis var. elegatiitula, Sehuchertella tenuis, Sir oph on ell a 



* Am. Geologist, vol. xvi, pp. 277 and 278, 1895. 



