The American Midland Naturalist 



PUBLISHED BI-MONTHLY BY THE UNIVERSITY 

 OF NOTRE DAME, NOTRE DAME, INDIANA 



VOL. VI. MAY, 1920. . NO. 



The Hackberry Stage of the Upper DevoniaB^;;?^ 



BY CARROLL LANE FENTON. 



I. ^Introductory. 



At what is commonly known as the Hackberry Grove Clay 

 Bank, in section 35, Portland Township, Cerro Gordo County, 

 Iowa, is the type locality of the formation described in this paper. 

 On the right bank of Lime Creek at that point is an escarpment 

 some seventy-five feet in height which is composed throughout its 

 exposed thickness of the rocks of two formations: the Hackberry 

 and the Sheffield.' These two formations comprise the" Lime Cresk 

 Stage" as defined by Calvin,^ but it is recognized, and was recognized 

 prior to Calvin's description, that the two formations are distinct. 



The nomenclature of these two formations had been considerably 

 involved, as has also been the assignment of geologic age. Hall, in 

 18,58^ assigned the beds of the Hackberry to the Hamilton Stage, 

 but in a later paper by Hall and Whitfield ^ they were considered 

 as being Chemung. White ^ referred the Hackberry shales to the 

 Hamilton, and H. S. Williams attempted at one time to show that 

 they were of Mississippian age,^ but later ^ corrected this. C. L. 

 Webster, in 1889,* referred the Hackberry to the upper Devonian, 

 but placed the subjacent shales in the Hamilton, but has corrected 



•Am. Jour. Sci. (4). XLVIII, pp. 355-376. 

 ^la. GeoL Surv. VII, pp. 161-192. 

 ^ Geol. of Iowa; Vol. I; pts. i and 2. 



•'Twenty-third Ann. Rep't, N. Y. State Cabinet, pp. 225-226. 

 5Rep't of Geol. Surv5. of State of Iowa, Vol. i, pp. 187-188; Vol. 2, 

 pp. 252-253. 



^Am. Jour. Sci. (3) ,XXV, pp. 97-104. 



^Loc. Cit., p. 311. 



*Am. Nat. XXIII, pp. 229-243. 



