20 D. K. Greger — Devonian of Central Missouri. 



Art. II. — The Devonian of Central Missouri {III). 

 The Cooper Limestone ; by Darling K. Greger, 



Under the name of Cooper marble this formation was 

 described by G. C. Swallow in 1855 in his . detailed re- 

 ports on Cooper and Marion connties. These reports 

 give a clear and concise description of the lithologic 

 characters of the formation, bnt having failed to find 

 it fossiliferous in the localities studied, Swallow tenta- 

 tively correlated it with the so-called Onondaga of 

 Montgomery and Warren counties. Apparently, how- 

 ever, he was never entirely satisfied with the disposi- 

 tion made of the formation, since we find him stating, 

 in his general discussion of the rocks of Missouri, that 

 there is a "mere possibility" that the Cooper marble 

 may be, in part at least, equivalent to the Trenton. 



This formation is best developed in Cooper and Pet- 

 tis counties, where it attains a thickness of approxi- 

 mately 25 feet. Limited outcrops occur, however, in 

 Boone, Moniteau and Marion counties, but in these it 

 seldom reaches its maximum depth. 



The writer has traversed all the streams in the coum 

 ties above named and examined every known outcrop 

 of the formation, and in 1916 at the Twenty-ninth An- 

 nual Meeting of the Geological Society of America, 

 announcement was made of the discovery of a distinc- 

 tive fauna in no wise related to the Devonian faunas 

 heretofore found in Missouri. The fossils of the 

 Cooper are for the most part new and undescribed 

 species, brachiopods are most abundant, but the large 

 Turbonopsis providencis (Broadhead) may be taken as 

 the guide fossil, its distribution throughout the forma- 

 tion being > quite common. 



The stratigraphic position of the Cooper may be better 

 understood from the following sections through Pettis 

 county eastward to Boone, where it thins out and finally 

 disappears. 



Section in Pettis county : The following measured 

 section, made in the near vicinity of Pinhook Bridge, 7 

 miles northeast of Sedalia, Pettis county, is considered 

 typical, since it gives a complete view of the lower and 

 upper contacts, both of which are marked by pronounced 

 unconformity. 



