BENTON FORMATION IN SOUTH DAKOTA 569 



The next paper was read by title : 



CARBONIFEROUS OF THE APPALACHIAN BASIN 

 BY JOHN J. STEVENSON 



The paper is printed as pages 37-210 of this volume. 

 The following paper was presented : 



FURTHER STUDIES OF OZARK STRATIGRAPHY 

 BY C. F. MARBUT 



The Society adjourned for the noon recess and lunch, and on reassem- 

 bling the first paper presented was : 



DEPOSITION OF THE APPALACHIAN POTTSVILLE 

 BY DAVID WHITE 



Remarks on the subject of the paper were made by I. C. White. The 

 paper is printed as pages 267-282 of this volume. 



The second paper was : 



BENTON FORMATION IN EASTERN SOUTH DAKOTA * 



BY J. E. TODD 



Contents 



Page 



Introductory 569 



Original Missouri River section reexamined 570 



Results , 570 



Correction of former interpretations 572 



Its geological extent 573 



Occurrence in adjacent states 574 



Introductory 



In the recent study of the geology of South Dakota by the members of the 



United States Geological Survey diverse interpretations have appeared. Mr Dar- 



ton's studies about the Black hills showed there 1,450 to 1,700 feet of Benton strata, 



while near Sioux City it had been counted 80 feet or less, and around Mitchell, 



where a sandstone which had been counted Dakota appears, it seemed virtually 



absent. Moreover, at the west the formation shows a threefold character, as 



follows : 



Feet 

 3. Carlile formation. Gray shales, with thin sandstones, limestones, and concretionary- 

 layers 500-750 



2. Greenhorn limestone. Impure, slabb}' limestone 50 



1. Graneros shale. Dark shale, with layers of massive sandstone in lower part in places. 900 



In the east, however, only shaly clay had been recognized. This was the more 

 remarkable, because the Greenhorn limestone described by Gilbert from Colorado, 

 and widely known in the Rocky Mountain region as the " Oyster-shell rim," would 

 from its fauna be specially likely to appear also along the shallow eastern margin 

 of the Cretaceous ocean. 



A suspicion that there was something wrong was further impressed by the find- 



* Printed by permission of the Director of the U. S. Geological Survey. 



