K1NDERH00K FORMA TIONS OF MISSO URI I 3 5 



to the effect that " to the south .... it underlies, directly, the 

 Phelps sandstone, the Sac limestone being absent." This manner 

 of occurrence would seem to indicate that the formation was but 

 a facies of the Sac limestone, it being thin or almost absent 

 where the typical facies of that formation is well developed, 

 becoming thicker and replacing the lithologic facies described 

 as the Sac limestone, to the south. A careful search for fossils 

 should be made in the limestone in order to determine whether 

 or not its fauna is the same as that in the Sac limestone. 



The typical facies of the Sac limestone is well exposed in 

 numerous outcrops along the Sac River and its branches in the 

 northern portion of Greene county, the name of the formation 

 being selected by Shepard * because of this occurrence. It is a 

 hard, bluish gray, compact limestone with a maximum thickness 

 of eighteen feet, usually deposited in beds of from six to ten 

 inches thick with thin greenish shaley partings between the beds. 

 The rock has been quarried somewhat extensively at several 

 points and shipped to Springfield to be used as curbing. Shepard 

 referred the formation with those beneath it, to the Devonian, 

 considering it to be of Hamilton age. No fossils were secured 

 by him in the formation itself by means of which such a correla- 

 tion could be established, but in the overlying Phelps sandstone, 

 numerous waterworn fragments of fish-teeth were secured, some 

 of which were identified as Ptyctodus calceolns. This genus of 

 fishes is usually considered to be limited to the Devonian, and 

 its presence in beds overlying the Sac limestone was considered 

 to be sufficient evidence to justify the reference of the under- 

 lying beds to the Devonian. A study of the invertebrate fauna 

 of the Sac limestone, however, serves to definitely correlate the 

 formation with the lower portion of the Chouteau limestone of 

 central Missouri, and leads to the conclusion that either the 

 waterworn fragments of fish-teeth have been wrongly identified, 

 or that the genus Ptyctodus has a higher geological range than 

 has hitherto been supposed. 



Although no fossil fauna was secured from this formation 



1 Loc. cit., p. 74. 



