2G8 C. R. KEYES DEVONIAN INTERVAL IN MISSOURI 



Introductory 



In centra] Missouri Carboniferous stratigraphy presents unusual rela- 

 tionships. Nowhere else in the whole region does the same succession 

 of Paleozoic terranes prevail. Beginning with the typical Chouteau 

 limestone as the basal member, the Carboniferous sequence rests directly 

 on Ordovician dolomites. In other parts of the state the hiatus is 

 represented b}^ extensive sections of Silurian and Devonian age. Of 

 these the last mentioned is by far the most important. In the region 

 contiguous the deposits laid down during the Devonian interval are in 

 many respects of exceptional interest. 



It is here purposed to regard the beds formed during the Devonian 

 interval as a formation having distinct individuality. While unequally 

 developed, it is not so indefinitely defined as has appeared at first glance 

 or as has been generally supposed. The ascribed vagueness has been found 

 to be due in great' measure to the fact of its being little understood. 



In the neighboring areas of uninterrupted sedimentation the sequence 

 comprises all those strata lying between the limestones about which 

 there has been but little doubt as to their Silurian age and the undoubted 

 Carboniferous limestones. The beds of this as yet not fully differentiated 

 terrane are commonly known as the " Niagara " dolomites. Above the 

 sequence is the great Mississippian series. 



The succession of beds thus stratigraphically delimited is believed to 

 be wholly representative of Devonian deposition. In the following pages 

 the reasons for this opinion are set forth. The conclusions arrived at, 

 while not novel, have never before been published. Exact information, 

 recently acquired, has so strongly confirmed the main suggestions that 

 some of the data on which they are based appear worthy of special note 

 at this time. 



The data relative to the northern part of the region were collected 

 partly under the auspices of the Iowa Geological Survey. The informa- 

 tion concerning the more southern district was secured mainly during 

 the prosecution of the work of the Missouri Geological Survey. Visits 

 were also made into the extreme southern portion of the region under 

 consideration and eastward into Illinois. 



It has no doubt often appeared strange that in the central Mississippi 

 valley, where the Silurian terranes are so well developed over such vast 

 areas and where the basal limestones of the Carboniferous are so sharply 

 cut off from the formations below, that our knowledge of the sediments 

 occupying the space between the two great systems should so long re- 

 main in such an unsatisfactory condition. However, as will appear, 



