138 STUART WELLE R 



From the list of fossils just given it will be seen that the 

 fauna of the Sac limestone corresponds closely with that of the 

 typical Chouteau limestone of central Missouri, and more espe- 

 cially with the lower division of the Chouteau limestone as 

 described by Swallow. 1 There is no foundation whatever for 

 correlating it with the Hamilton formation of the Devonian, but 

 several of the species are also present in beds 5 and 6 of the 

 Kinderhook at Burlington, Iowa. 



The formation referred by Shepard to the Louisiana lime- 

 stone, is described as follows by that author : 2 



The lowest member of the Carboniferous is not so variable in composi- 

 tion and texture as the other two. It frequently, however, possesses such 

 lithologic characters as to make it difficult to distinguish it from the asso- 

 ciated Devonian rocks. As only a few obscure fossils have been found in 

 this region, its identification is dependent entirely upon position and lithologic 

 characters. 



The Devonian formation referred to in the above quotation is 

 the Sac limestone. The difficulty in separating the so-called 

 Louisiana limestone from the Sac limestone is frequently indi- 

 cated by Shepard by such statements as the following : 



P. 85 : .... an outcropping of what seems to be some eight or ten 

 feet of Louisiana, though it may prove to be a somewhat modified form of 

 Sac limestone ; p. 76 : it is barely possible that this particular rock may be 

 Louisiana, and not the Sac limestone ; p. 77 : there is frequent difficulty, on 

 account of lithologic characters, in separating it [the Sac limestone] from the 

 Louisiana when the Phelps sandstone is absent ; p. 77 : it is a noticeable fact 

 that, when the Devonian [the Sac limestone] is present, the Louisiana lime- 

 stone is usually, though not always, absent. 



Among the localities mentioned for the Louisiana limestone, 

 the best exposure where both this formation and the Sac lime- 

 stone are present, is said to be at the Newton mound, 3 and the 

 description of its stratigraphic position at this locality is as fol- 

 lows : "Immediately underlying the Hannibal shales and over- 

 lying the Phelps sandstone, are ten feet of this limestone." The 

 Phelps sandstone at this same locality is described in another 



'Geol. Surv. Mo., Rep. I and II (1855), p. 102. 



2 Loc. cit., p. 84. 3 Loc. cit., p. 84. 



