HACKBERRY STAGE OF THE UPPER DEVONIAN. 



i8i 



for the shales below the Hackberry, and (3), that the name "Lime 

 Creek" is not only unsuitable, but is preoccupied, and so should 

 be dropped. 



Fig. I. — Correlation of Nomenclatures. 



II. — Stratigraphy and Distribution. 



There is no point at which a satisfactory section of the Hackberry 

 Stage may be taken. The following section, a compilation giving the 

 maximum thicknesses observed, is here introduced in order to 

 facilitate reference in the following description. 



II. A. — General Section of the Hackberry Stage.' 

 II. — Owen Substage. 



C. — Acervularia Zone. 



Calcareous, light gray limestones, containing Pachyphylluni, Alveolites, 

 Acervularia (an undescribed species; typical of the zone) Stromato- 

 porella, Syringoslroma, and other species, corals and Stromatoporoids 

 being the most abundant forms 20 



B. — Naticopsis Zone. 



Magnesian shales and limestones, and argillaceous dolomitic limestones, 

 usually dark buff or brownish in color. Gastropods the predominating 

 fossils, Westernia and Naticopsis the predominating genera; Naticopsis 

 gigantea H. & W. the most typical species 30 



A. — Idiostroma Zone. 



Buff, gray-buff, or buff-brown limestones, heavily bedded. Crowded 

 throughout by two species of Stromatoporoids (?) commonly referred 

 to Idiostroma, as well as other Slromaloporoida, and several species of 



gastropods 4-6 K 



I. — Cerro Gordo Substage. 



B. — Spirifer Zone. 



Yellowish, very calcereous shales, shaley clays, and shaley limestones 

 Weathers partly to clay, partly to limestone chips. Abundantly fos. 



'For comparison with Calvin's section in la. Geol. Sun. VII., p. 163. 



