BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 32, pp. 437-478, PLS. 7-12 DECEMBER 1, 1921 



SWEET GKASS HILLS, MONTANA ^ 



BY JAMES F. KEMP AND PAUL BILLINGSLEY 



{Presented before the Society by the senior author December 31, 1919) 



CONTENTS 



Page 



Introduction 437 



Review of earlier work 440 



Investigations of George M. Dawson 440 



Resenrclies of Frank D. Adams, W. H. Weed, and L. V. Pirsson 441 



Work of A. R. Ledoux 443 



General iDetrography 443 



Structural and stratigraphical relations 445 



General review 445 



West Butte 446 



Middle Butte 450 



East Butte 453 



Some petrographic details 456 



Tinguaite 456 



Minette 458 



Contact effects 461 



Other economic resources 462 



Sedimentary rocks 463 



Stratigraphy 463 



Mississippian 463 



The section 463 



Madison limestone 466 



Overlying unconformity 466 



Jurassic — Ellis formation 468 



Lower Cretaceous — Kootenai formation 468 



Upper Cretaceous 471 



Colorado groui) 471 



Montana group 476 



Glacial drift 478 



Introduction 



The Sweet Grass Hills are a group of three separate laccolith ic centers 

 in the northern part of Toole County, Montana, and almost touching the 



^ Manuscript received by the Secretary of tlie Society August liii, l".)::i. 



(437) 



