BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 23, pp. 463-470, PLS. 25-27 SEPTEMBER 26, 1912 



PKE-\VlSC0iS81A' CHANNELS IN SOUTHEASTEKX SOU^ni 

 DAKOTA AND NOKTHEASTEJiN NEBEASKA ^ 



BY J. E. TODD 



{Presented before the Society December 2S, lUll) 



CONTENTS 



Geueral relations 4fv> 



Chanuels of the earlier stage , 4(>4 



The Creightoii-Plalnview channel 4G4 



The Hartington-Coleridge channel 464 



Chanuels of the later stage 460 



General conditions , 466 



The ancient Niobrara , 460 



The ancient Ponca 467 



The ancient Mosquito 468 



The ancient Choteau 469 



Conclusions 470 



General Relations 



Xcai"ly M) years ago it was discovei'od that in the early Pleistocene the 

 master stream of the soiitlieasterji South Dakota region followed the 

 \alley of James River to its present mouth and then the Missouri helow, 

 and also that the present course of the Missouri above Yankton was out- 

 lined around the edge of the great iee-sheet as late as the \\'isconsin 

 stage. 



Later studies made iji preparing the Elk Point folio led the writer lo 

 the couclusion that there had been an earlier advance of the ice-sheet 

 down the James River A'alley at a time when the drainage level was 

 about 100 feet higher than at present. Whether this was during the 

 Kansan stage or the Towan stage has not been determined, hut i)rohably 

 it was during the Kausau. At that stage the Dakota lobe extended as 

 far south as West Point, Xebraska, and the di-ainage from the west side 



^Manuscript rorcivcd by tlie Sccrotni-y (if the Society .Taniiary lit. I'.irj. 



( 4(S8 



