46 IOWA GEOLOGICAL SURVEY 



sponds more or less closely with that of the Hamilton in the more 

 eastern ("Ohian") region.* To the Upper Devonian were re- 

 ferred two units — the Sweetland Creek shales, and the State 

 Quarry limestone — which rest unconformably upon the Cedar 

 Valley limestone, and occur as outliers in the east central part 

 of the State. The former of these is developed chiefly in Mus- 

 catine county, and the latter in Johnson county northward of 

 Iowa City. A scheme of classification adopted in earlier volumes 

 of the Survey Reports is reproduced immediately hereinafter 

 for the purpose of showing the succession of Middle Devonian 

 sediments as they have been commonly interpreted until within 

 the past year or two. Conformably, however, to Professor Cal- 

 vin's most recent interpretation of the Lime Creek shales, based 

 upon a study of their f aunal relations, they are now assigned a 

 somewhat higher stratigraphic position. This change is indi- 

 cated in the second synoptical table presented herewith, which 

 is reproduced from Professor Calvin's "Notes on the Geological 

 Section of Iowa" (Journ. Geol., 1906, vol. 14, p. 572). In connec- 

 tion with the latter it is necessary to bear in mind the following 

 statement of the author by way of explaining the succession: 

 "The three units referred to the Upper Devonian — the Sweet- 

 land Creek shales, Lime Creek shales, and State Quarry lime- 

 stone — do not lie one above the other, but each is developed 

 locally and lies uncomf ormably on the Cedar Valley limestones. ' ' 



* Calvin, S. On the fauna found at Lime Creek, Iowa, and its relation to other 

 geological faunas. Araer. Journ. Sci. (1883), 25, pp. 432-436. — Idem, Devonian 

 System (in Geology of Buchanan county). Rept. Iowa Geol. Surv. (1898), vol. 

 VII, p. 221. 



