CHOUTEAU LIMESTONE 113 



TERRANAL AFFINITIES OF ORIGINAL CHOUTEAU 

 LIMESTONE. 



CHARLES KEYES. 



In all the Mississippi valley there is no geologic formation 

 that is so misunderstood, or so illy considered as regards its 

 stratigraphic relations, as the massive, buff limestone terrane 

 immediately underlying the Burlington limestone of Missouri 

 and Iowa. Originally noticed by Prof. G. C. Swallow, 1 in 1855, 

 as a thick, homogeneous lithologic unit typically developed in 

 central Missouri along the northern flanks of the Ozark dome, 

 and extended into other parts of the state as the uppermost 

 member of a tripartite "Chemung" group, little mention is 

 later made of it. 



When, a generation after Swallow, Prof. H. S. Williams 2 

 revived the title it was with an entirely different meaning; the 

 term then applying not to a terrane at all but to a fauna carried 

 by all of the Early Carboniferous rock-section beneath the 

 Burlington horizon. In this he followed Prof. G. C. Broad- 

 head 3 who had, in 1874, proposed the name Chouteau Group to 

 take the place of Chemung Group of the previous accounts of the 

 region. In the earlier reports of the present Geological Survey 

 of Missouri 4 the term, in Swallow's original sense', is repeatedly 

 recognized. Prof. E. M. Shepard reports 5 the. formation in 

 its typical development to occur in Greene county, in south- 

 western Missouri. In the north, in Iowa, the Chouteau lime- 

 stone is not generally recognized by title, yet it is several times 

 so called in the central part of the state. 



In Illinois, where the Chouteau limestone is not known to 

 be represented, the terrane is commonly merged with the Kind- 

 erhook group, as is done by F. B. Meek and A. II. Worthen 7 . 

 Through the wide usage of the latter title Swallow's name is 



1 Missouri Geol. Surv., 1st and 2d Ann. Repts., p. 102, 1855. 



2 Bull. 80, U. S. G. S., p. 169, 1891. 



3 Missouri Geol. Surv., Rept. 1873-4. p. 26, 1874. 



^Missouri Geol. Surv., Vol. IV, p. 57, 1894. 



5 Ibid., Vol. XII, 1898. 



c Iowa Geol. Surv., Vol. XXII. p. 154, 1913. 



'Am. Jour. Sci., (2), Vol. XXXII, p. 28S, 1861. 



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