I§0 THE AMERICAN MIDLAND NATURALIST 



the latter error in later papers. By the Iowa Survey the "Lime 

 Creek" has been consistently and correctly assigned to the upper 

 Devonian. In a recent paper by myself,^ Webster and I referred 

 the shales below the Hackberry to a possible Genesee time equiva- 

 lency; in 1919^ I applied the name Sheffield to these shales, but 

 expressed no opinion as to their age except that they are of the 

 late upper Devonian. 



Webster, in 1889,^ in a paper on the Devonian of Iowa, divided 

 it into three stages, the Corniferous, the Hamilton, and the Hack- 

 berry. His Hackberry Group was stated by him to consist of one 

 formation which "is known to attain a thickness of forty-five feet, 

 and is made up, for the greater part, of a yellowish brown argil- 

 laceous, and sometimes arenaceous shaley limestone." This forma- 

 tion was stated to be the highest Devonian in the state, and, while 

 the description leaves much to be desired, there is no doubt that 

 Webster's Hackberry Group, as originally described by him, 

 includes all of the Devonian rocks above the blue shale at Hack- 

 bierry Grove, Rockford, and other localities, and below the Kinder- 

 hook. 



Prior to 1889 the names "Rockford Shales," "Lime Creek 

 Shales," and "Lime Creek Beds" had been used by various authors. 

 Calvin and Williams used all three interchangeably; Webster 

 used the term "Rockford Shales." This name, however, was pre- 

 occupied by another formation, so had to be abandoned. 



In 1897^ Calvin, in his report on the geology of Cerro Gordo 

 County described the shales and limestones above what was then 

 considered to be the Cedar Valley Limestone'' as the Lime Creek 

 Stage, and this name has been used in the Iowa reports, and is 

 more widely known than the name proposed by Webster. In 

 1919,5 I discussed the nomenclature of the two formations in ques- 

 tion, attempting to show that: (i) The name "Lime Creek" 

 as used by the Iowa Survey does not equal " Hackberry" as used 

 by Webster and myself; (2) that a new formation name w^as needed 



'Am. Mid. Nat. V. p. 214. 



^See Note 8. The division of the Devonian below the Hackberry into 

 Hamilton and Corniferous was erroneous. 



■^a. Geol. Surv. VII., pp. 161-170. 



■'The Nora Limestone of Thomas (Science, N. S., XXXVII, p. 459 was 

 not separated from the Cedar Valley limestones at that time. 



5Loc. cit. pp. 355-360. 



