C. L. Fenton — The Devonian of Iowa. 



Aet. XXIV. — The Hackberry Stage of the Upper Devo- 

 nian of Iowa; by Caekoll Lane Fenton. 



Introduction. 



At what is commonly called the Hackberry Grove clay 

 bank, in the northeast quarter of section 35, Portland 

 township, Cerro Gordo County, Iowa, is the type locality 

 of the formation discussed in this paper. On the right 

 bank of Lime Creek at this point is an escarpment some 

 seventy-five feet in height, consisting throughout its 

 entire exposed thickness of two formations : the Hack- 

 berry and the Sheffield. These two formations compose 

 what Calvin called the Lime Creek Stage, but aside from 

 the fact that both are members of the Upper Devonian 

 there is very little connection between the two. 



A. The Name "Hackberry." 



In 1889 there appeared, in the American Naturalist 

 (vol. 23, pp. 229-243), a paper by Clement L. Webster 

 entitled "A General Preliminary Description of the Devo- 

 nian Rocks of Iowa ; which constitute a typical section of 

 the Devonian Formation of the Interior Continental Area 

 of North America. ' ' In this paper both of the formations 

 exposed at Hackberry Grove were described, that which 

 I have referred to as the Sheffield being placed as Hamil- 

 ton in age. The " Hackberry Group" as proposed by 

 Webster in this paper "is known to attain a thickness 

 of forty-five feet, and is made up, for the greater part, of 

 a yellowish brown argillaceous, and sometimes arena- 

 ceous, shaly limestone''; this formation also is the high- 

 est division of the rocks of this age [the Devonian] in 

 the state. Detailed faunal lists are given by Webster, 

 and the formation was described as fully as the condition 

 of the exposures at that time would permit. In later 

 papers Webster gave additional information regarding 

 this formation. 



, In 1897, Calvin (Iowa Geol. Survey, vol. VII) pub- 

 lished a description of what he called the "Lime Creek 

 Stage,' ' which according to his definition includes not 

 only the Hackberry Stage of this paper but also the Shef- 

 field formation. Calvin applied the name "Owen Sub- 

 stage' ? to those rocks here placed in that division, and 



Am. Jour. Sci. — Fourth Series, Vol. XLVIIT, No. 287.— November, 1919. 

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