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



There is no doubt that the place of the Bowling Green 

 limestone member of the Edgewood formation in the geologic 

 column is below the Sexton Creek limestone, which from its 

 fossils is known to be of about Brassfield age. 



Alexandrian strata in Iowa and northwest Illinois. 



The Winston limestone. — Strata nearly equivalent in time 

 to the Edgewood and Sexton Creek limestones, respectively, 

 of northeastern and southern Illinois and eastern Missouri, 

 have been found in Jo Daviess and Carroll Counties, Illinois, 

 and in northeastern Iowa. However, the early Silurian strata 

 in northwest Illinois and in Iowa present such different aspects 

 and show such differences in their faunas compared with the 

 normal Edgewood and Sexton Creek limestones, as to make it 

 probable that they were deposited in a sea that advanced upon 

 the region from the north, as were the overlying Niagaran 

 dolomites in the same region. 



Early Silurian strata representing the Edgewood period of 

 deposition were first recognized in Jo Daviess County in an 

 exposure about six miles southeast of Galena Junction, in the 

 cut at the station of Winston at the south end of the tunnel 

 made by the Chicago Great "Western railroad, where the fol- 

 lowing section was made : 



Section at Winston, at south end of Chicago Great Western tunnel. 

 Alexandrian limestone Feet 



3. Dolomite, yellow, earthy, fine-grained, in rather 



thin, even layers _ 22 



2. Sandstone, bluish, calcareous, and shaly ; con- 

 spicuously laminated J \ 



A break in sedimentation. 

 Maquoketa sbale 



1 . Shale, bluish gray, without fossils V 



In the above section members 2 and 3 furnished the fossils 

 Lingula sp., Orbiculoidea sp., Plectamhonites sp., Schucher- 

 tella sp., Dalmanella edgewoodensis, Atrypa putilla, Atrypa 

 prmnarginalis, Camarotoechia f cf. concinna, Calymene sp., 

 Encrinnrus sp., and P rosins determinatus. 



Of the above species, Dalmanella edgewoodensis, Atrypa 

 putilla, Atrypa prcemar gin alls, Camarotmchia? concmna, 

 and Praetus determinates denote the Edgewood age of the 

 strata, but the absence of such fossils as Lyellia thebesensis, 

 Rhynchotreta thebesensis, Whilfieldella oroides, Cyp)haspis 

 intermedia, and other characteristic Edgewood species which 



