RECENT DISCOVERIES OF CAMBRIAN BEDS IN THE 

 NORTHWESTERN UNITED STATES 



By CHARLES ELMER RESSER 

 Curator, Division of Invcrfcbrate Paleontology, U.S. National Museum 



The lifelong studies of Dr. Charles D. Walcott on the stratigraphy 

 and paleontology of Cordilleran North America not only made this 

 a classic area for geologic research, but also established here the most 

 complete known sections of Cambrian strata. However, a considerable 

 area in which Cambrian strata seem to be wanting existed between the 

 definitely known outcrops of the Cambrian in Montana and in British 

 Columbia. Dr. Walcott's further plans included field work in the 

 northern United States and southern Canada for the investigation of 

 this problem, but his death prevented the completion of the project. 



Recently, several fortunate discoveries of Cambrian beds have been 

 made in northwestern United States which contribute to a better 

 understanding of the fundamental structure of the Rocky Mountain 

 region. To understand fully the significance of these recent discoveries 

 it is necessary to have in mind both the geographic distribution of the 

 concerned Cambrian outcrops, as well as the primary structural regions 

 of the Cordilleras, especially with respect to the location and direction 

 of geosynclines and basins at the beginning of Paleozoic sedimentation. 



PREVIOUSLY KNOWN DISTRIBUTION OF THE CAMBRIAN 



Hitherto, as a result of Walcott's extensive studies, the Lower 

 Cambrian was known to extend from southern California northward 

 through the Great Basin as far as the Eureka District in central 

 Nevada and the vicinity of Salt Lake City in the Wasatch Range of 

 Utah. From these points northward, beds older than Middle Cam- 

 brian seemed to be lacking, not only in northern Utah, Idaho, and 

 Montana, but also for a considerable distance along the southern part 

 of the Canadian Rockies. 



The Middle Cambrian, on the other hand, was known to extend 

 beyond the mentioned points in Nevada and Utah, throughout the 

 Wasatch and thence northward into the western side of the Teton 

 Range, in western Wyoming, and to crop out widely about the head- 

 waters of the streams forming the Missouri River in western Mon- 



Smithsonian Miscellaneous Collections, Vol.92, N0.10 



