IOWA ACADEMY OF SCIENCES. 105 



A DEVONIAN HIATUS IN THE CONTINENTAL IN- 

 TERIOR ITS CHARACTER AND DEPOSITIONAL 

 EQUIVALENTS. 



BY CHARLES R. KEYES. 



In Iowa, with our nearly 500 feet of Devonian sediments, 

 we are not apt to think very much about a possibility 

 of the lack of this great system soon after the boundaries 

 of our state are passed. Yet the possibility is an actuality. 

 In west-central Missouri it has been lately found that no 

 rocks of Devonian a^e are represented. The lower Carbon- 

 iferous strata rests directly upon Ordovician dolomites. 



The general section east of Clinton, Missouri, on Grand 

 river, a tributary of the Osage, is as follows: 



FEET. 



Henrietta limestones 60 



Cherokee shales (Dos Moines series) 100 



Augusta limestone ; 175 



Chouteau limestone (Mississippian series) 15 



Ordovician dolomite (exposed) 20 



This gap in sedimentation in west-central Missouri in- 

 cludes, as is shown, more than the Devonian alone. The 

 whole of the Silurian is absent. But only the Devonian 

 portion is considered at this time for the reason that im- 

 portant correlations have been recently made, and these 

 bear directly upon the nature of the hiatus. 



Southward, in southwest Missouri, the Devonian strata 

 again put in their appearance. In northern Arkansas Wil- 

 liams has also lately demonstrated that both Devonian and 

 Silurian sediments were laid down in this part of the 

 region. On the east side of the Ozark plateau, along the 

 Mississippi river, both Silurian and Devonian sequences 

 are unbroken. 



81 A S 



