THE PTARMIGANIA STRATA OF THE NORTHERN 

 WASATCH MOUNTAINS 



By CHARLES ELMER RESSER 



Curator, Division of Stratigraphic Paleontology 



U. S. National Museum 



(With 14 Plates) 



INTRODUCTION 



An interesting fauna occurs in the lowermost Middle Cambrian 

 beds at several places in the northern Wasatch Mountains of Idaho 

 and Utah. The fauna is characterized by great variety of species 

 and genera, and the numerous individuals are excellently preserved, 

 chiefly in crystalline limestone. Most of the material here described 

 was collected by Walcott in 1898 and 1906. When I came to Wash- 

 ington in 1914 as Dr. Walcott's assistant, the first task assigned to 

 me was the preparation of this material. 



Two classes of data are necessary for the advancement of 

 stratigraphy : First, there must be a sufficient number of sections, 

 measured at strategic points, to furnish knowledge of areal extent 

 and of variations in lithology and in thickness of the sheets of sedi- 

 ment that constitute the formations ; second, it is necessary to know 

 the faunas characterizing the formations. This paper describes 

 another fauna but also discusses some stratigraphic problems. Un- 

 fortunately the stratigraphic terminology of the Wasatch Mountains 

 is not fully satisfactory ; hence a hybrid faunal-stratigraphic title 

 is used. 



Recently the related fauna in the superjacent Spence shale was 

 described (Resser, 1939). Taken together these faunas should enable 

 the building of the early Middle Cambrian portion of the column 

 with greater precision, not only locally but throughout the Cor- 

 dilleran region. 



Sections of Middle Cambrian rocks were measured in the northern 

 Wasatch Mountains by Walcott in 1898 and 1906 and subsequently 

 by other geologists. The only detailed mapping in the region is that 



Smithsonian Miscellaneous Collections, Vol. 98, No. 24 



