219 Devonian of Southern Indiana 91 



In 1 861 Meek and Worthen-'^ published a paper on the age of 

 the Goniatite limestone at Rockford, Ind. The erroneous asser- 

 tion of Christy that the Rockford limestone is central in the 

 Black shale is corrected by these authors, who state that the 

 Black shale lies entirely below the limestone. The Rockford 

 limestone is identified by them to be of the same age as the Chou- 

 teau limestone of Missouri. This determination is based upon 

 the identification of at least six of the twenty-three or twenty- 

 four known Rockford species with characteristic Chouteau spe- 

 cies. These species are Naiitibis digomis M. and W., Euompha- 

 his lens Hall, RhychoncUa missoziriciisis Shumard, Spirifcr coopcr- 

 <'7/mSwall., Cardiopsis radiata M. and W., Q.n6. Sphnioptct'iuiii 

 c nor me M. and W. 



It seems to the writer that in correlating the Rockford lime- 

 stone with other formations in the Mississippi valley considerable 

 weight should be given to the stratigraphic evidence, since it lies 

 directly above the Black shale, a formation which may be readily 

 recognized throughout most of the Paleozoic area of the Missis- 

 sippi valley. Should the stratigraphic evidence be given princi- 

 pal weight, the Rockford limestone would be correlated not with 

 the Chouteau, but with the Lithographic limestone. Both the 

 Rockford and the Lithographic limestones lie immediately above 

 the Black shale. Both are rather local in their extent. The 

 lithological description given by Worthen of the Lithographic 

 limestone is in part as follows: "It is usually of a light bluish- 

 green or dove color, weathering to a drab. It breaks walh a 

 smooth conchoidal fracture, "f It would be difficult to give a 

 better physical description of the Rockford limestone of Southern 

 Indiana than this. The Lithographic limestone is stated by these 

 authors to be "rather local, ";{; which is also a characteristic of the 

 Rockford limestone. 



The following .section|| is given of the Missouri beds: 



*Am. Jour. Sci., 2d ser., vol. 32, p. 167. 

 tGeol. Surv. of 111., vol. i, p. 114. 

 JAm. Jour. Sci., vol. 32, 2(1 sen, p. 170. 

 ||Ib. 



