290 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



K 15. IOWA. 



The following section of the Devonian of Iowa was compiled by Chamber- 

 }j^i34o fpQjj^ ^}^g Iowa Siirvey reports : 



Generalised section of the Devonian for Iowa. 



These strata represent Middle and Upper Devonian, a local unconformity or 

 change in fauna distinguiching the two. The Middle Devonian beds overlap north- 

 ward as they rise in the series and rest in part on Silurian, in part on Ordovician. 

 Calvin "^ states with reference to strata in the extreme northern part of the State : 



The lowest beds seen in Howard County belong to a horizon far above what has been 

 recognized as the base of the Devonian in the southern part of the area of its distribution. 

 The beds which rest directly on the Maquoketa contaia StropTieodonta demissa Conrad, Pro- 

 ductella suhalata HaU, Atrypa aspera Schlot., Spirifer pennatus Owen, and Cyrtivu TMmiltonensis 

 HaU. The fauna indicates a horizon equivalent to that represented about the middle of the 

 quarries at Independence, in Buchanan, County. In this zone in Howard County, ProducteUa 

 is the most abundant and most characteristic fossil, and it is convenient to refer to the horizon 

 as the ProducteUa beds. This zone belongs to the Upper Davenport beds of Norton, below 

 which, before reaching the base of the Devonian in Linn, Cedar, and Scott counties, there are 

 divisions of the Wapsipinicon stage which have been described as Lower Davenport, Inde- 

 pendence, Otis, and Coggan. 



With reference to the distinction of Devonian and Carboniferous WeUer *" 

 concludes : 



The succession of faunas exhibits a somewhat gradual transition from the earher faunas 

 with quite marked Devonian characters to the later ones which are typically Carboniferous 

 in aspect. The Devonian element in the faunas is for the most part exhibited by the pelecypods, 

 while the brachiopods are usually Carboniferous in aspect. This overlapping and interminghng 

 of Devonian and Carboniferous faunal elements makes it impossible to draw a sharp line sepa- 

 rating the Devonian and Carboniferous systems such as is recognized in the continental interior 

 between the Ordovician and Silurian in the Medina formation, and between the Silurian and 

 Devonian in the Waterhme formation. The Devonian-Carboniferous dividing line is more 

 nearly analogous with the Cambro-Ordovician division. 



K 16. WISCONSIN. 



In the vicinity of Milwaukee the Devonian is represented by the MUwaukee 

 formation (of Hamilton age). According to Alden, " as nearly as can be deter- 

 mined from partial exposures and drilled wells the order and maximum thickness 

 of the members of the formation are as follows: 



