BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 24, PP. 607-624, PLS. 28-35 DECEMBER 22, 1913 



PROCEEDINGS OF THE PALEONTOLOGICAL SOCIETY 



OKIGIN OF THE BIGHOKN DOLOMITE OF WYOMING x 



BY ELIOT BLACKWELDER 



(Read before the Paleontological Society December SI, 1912) 



CONTENTS 



Page 



Introduction 607 



Topographic expression 607 



Distribution 609 



Geologic age 610 



General characteristics 610 



Interpretation 613 



General significance 613 



Origin of the structures 614 



Why the rock is a dolomite 618 



Summary 624 



Introduction 



topographic expression 



Among all the sedimentary formations in Wyoming there is probably 

 none more persistently and fully exposed along its outcrops than the 

 early Paleozoic dolomite, which Darton 2 has called the Bighorn limestone. 

 So massive are its beds that in many places it seems to consist of but a 

 single stratum 100 to 300 feet thick. By breaking off along vertical 

 joints the formation leaves continuous and often impassable cliffs where 

 the beds are not highly inclined, or rises in sharp "hogback" ridges where 

 the dip is steep. Other Paleozoic terranes, such as the Madison limestone 

 and the Tensleep sandstone, make cliffs and ridges, but none so uniform 

 and persistent as the Bighorn dolomite. The individuality of its expo- 



1 Published by permission of the Director of the U. S. Geological Survey. A prelimi- 

 nary digest of this paper was presented at the meeting of the Geological Society of 

 America at New Haven in December, 1912. (See Bull. Geol. Soc. Am., vol. 24, 1013, p. 

 115.) 



* N. H. Darton: Geology of the Bighorn Mountains of Wyoming. U. S. Geological 

 Survey, Professional Paper No. 51, 1906, 



(607) 



