360 C. L. Fenton—The Hackberry Stage of 



with a formation that differs in no essential from the 

 Hackberry Group of Webster, though it does differ from 

 the Lime Creek of the Iowa Survey. In addition I have 

 the reasons that I have above set forth. I think this 

 explains why the term "Hackberry" is nsed by me 

 rather than "Lime Creek." 



B. The Stratigraphy and Distribution of the Hackberry. 



At no one point can a satisfactory section of the full 

 Hackberry Stage, as developed in Iowa, be taken. The 

 two type localities — Hackberry Grove, for the entire 

 stage; Owen Grove for the Owen Sub-stage — together 

 with comparisons with points other than these give the 

 complete section. To make reference more satisfactory, 

 the general section of the formation is given here. 



General Section of the Hackberry Stage. 

 II. — Owen Sub-stage. Feet 



Acervnlaria Zone. 



Calcareous, light gray limestones, containing Pachyphyllum, 

 Alveolites, and other corals, in large numbers, an unde- 

 scribed species of Acervnlaria being the most distinc- 

 tive 20 



Naticopsis Zone. 



Magnesian shales and limestones, and argillaceous dolomitic 

 limestones, often dark buff or brownish in color. Contains 

 numerous fossils, with gastropods predominating, Naticopsis 

 gig ant ea H. & W. the most characteristic species 30 



Idiostroma Zone. 



Buff or buff-brown, heavily bedded limestones. Contain 

 great masses of two species of Idiostroma{ ?), as well as 8. 

 incrustans (H. & W.), S. solidula (H. & W.), and gas- 

 tropods 4-6% 



I. — Cerro Gordo Sub-stage. 



Spirifer Zone. 



Yellowish, very calcareous shales, shaly clays, and occa- 

 sional bands of shaly limestone. Weathers partly to clay, 

 and partly to chips or nodules. Extremely fossilif- 

 erous 20 



Striatula Zone. 



Calcareous shales, and shaly limestones, slightly gritty, too 

 much so ; contains large amounts of iron pyrite, and near the 

 base often contains large numbers of calcareous concretions. 

 Fossiliferous, but species limitecl, and usually represented 



by casts 25 



Unconformity.* 

 (Sheffield Formation underlying) 



* There may be some question as to whether this contact is unconform- 

 able or disconformable. Webster considers the former to be more probable. 



