INTERVAL FORMATIONS 273 



ited lense included in a huge shale formation. The upper part of this 

 shale is called in Missouri the Hannibal terrane, and the lower part the 

 Grassy Creek formation. At Burlington the two shale beds, which far- 

 ther south are so distinct and separated by a great limestone, form a 

 single unbroken shale sequence. The faunas contained in the several 

 component formations are fully discussed farther on. 



HIATUS OF WEST-CENTRAL MISSOURI 



On the west flank of the Ozarks, Devonian deposition appears to be 

 entirely wanting. Near Sedalia the beds are very thin. Farther south, 

 near Clinton, the sections show the Carboniferous limestones resting 

 directly on the Orclovician, as has been so well demonstrated b}^ Mar- 

 but* The explanation of this fact has not yet been determined satis- 

 factorily. There have been difficulties in the way of direct observation 

 in those districts in which inquiries have been carried on, and opportu- 

 nity has not been given to conduct the search in neighboring localities. 



DEVONO-CARBONIFEROUS IN SOUTHWEST MISSOURI 



The manifest tendency of late years to throw together the Devonian 

 and Carboniferous beds of southwest Missouri merely because there have 

 existed slight differences of opinion among various observers as to the 

 geological age of some of the unimportant layers does not appear to be 

 conducive of the results hoped for. The attempts to make up for insuf- 

 ficient observation by merging formations realty distinct under a single 

 name not only does not solve the various problems presented, but merely 

 defers and makes harder the solutions. What is really needed is clear 

 differentiation, clear delimitation, and clear definition of the several 

 terranes. 



As given by Shepard,f the general section of the Interval representa- 

 tives in southwestern Missouri is as follows : 



Southwest Missouri Section 



Feet 



Hannibal shales 90 



Louisiana limestone 10 



Phelps sandstone 15 



Sac limestone 15 



King limestone 15 



Eureka shale 10 



The typical Chouteau limestone appears to be well represented above 

 the so-called Hannibal shales, and has a thickness of often 30 feet. The 



♦Missouri Geol. Survey, vol. xii, 189S, part ii, p. 121. . 

 f Missouri Geol. Survey, vol. xii, 1898, p. 49. 



