BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 1, pp. 245-286 April 7, 1890 



OROGRAPHIC MOVEMENTS IN THE ROCKY MOUNTAINS. 



BY S. F. EMMONS. 

 (Read before the Society December 26, 1880.) 



CONTENTS. 



Page. 



Introduction and Historical Review 245 



Pre- Cambrian Land . 256 



Early Palaeozoic Land 259 



The Late Palaeozoic Movement 2(31 



Late Palaeozoic Land 263 



The Jurassic Movement 267 



Jurassic Land 209 



The Post-Cretaceous Movement 280 



Introduction and Historical Review. 



That the vast succession of mountain ranges and elevated plateaus and 

 valleys which go to make up the Cordilleran mountain system in the United 

 States must be the final result of a number of orographic movements occur- 

 ring at different periods of the earth's history was recognized in the earliest 

 geological explorations in that region by Marcou, Newberry, Le Conte, and 

 others. It was not, however, until systematic examination of large areas, 

 both topographical and geological, had been instituted, which permitted the 

 construction of geological maps of a substantial degree of accuracy, that 

 any attempt could be made to determine the number and comparative im- 

 portance of these movements and their relative position in the structural 

 history of the region. Even then the conditions under which such exami- 

 nations were conducted, necessitating the covering of large areas in a given 

 time, which time was dependent more upon the geographical extent of the 

 area than upon the complexity or relative importance of its geological struct- 

 ure, did not admit of an exhaustive study, and many significant facts were 

 necessarily overlooked. 



It will only be when the whole Cordilleran region shall have been accu- 

 rately surveyed with much greater detail than has hitherto been practicable 

 that its complete and accurate history can be written. Meantime much 

 additional light can be thrown upon the subject by detailed examination of 



XXXIII— Bun. Gkoi,. 80c. Am., Vol. 1, 1889. (245) 



