2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



of the Randolph quadrangle, which includes the eastern slopes of 

 the Bear River Range. That report is in press. Without detailed 

 mapping of a considerable area, it is not possible to understand fully 

 the stratigraphic relations, for the early Middle Cambrian sequence 

 may be incomplete, and some of the formations seem to vary in 

 thickness and lithology more than usual for Cambrian strata in the 

 central Cordilleran region. 



In 1906 Walcott measured the Cambrian strata at four widely 

 separated points but published the results as a single composite 

 section (1908a, b). This obscured variations in lithology and thick- 

 ness and made correlation uncertain. If, however, we go back to the 

 original field notes, thereby getting away from the confusion intro- 

 duced with the composite section, several facts became clear. Deiss 

 (1938) remeasured the Blacksmith Fork section and discussed the 

 stratigraphy and stratigraphic terminology in the light of the informa- 

 tion yielded by that one section. 



With a better understanding of the Spence shale and immediately 

 subjacent Ptarmigania faunas and by using information from related 

 sections, as well as the results of mapping of the Randolph quad- 

 rangle, it is now possible to advance a step or two toward a solution 

 of the Middle Cambrian stratigraphy of the northern Wasatch region. 



At first it was planned to publish only the fossil descriptions, but 

 as the work progressed it became increasingly desirable to determine 

 stratigraphic relationships so that the faunal affinities could be better 

 understood. Seemingly there is yet much to learn concerning the 

 composition and position of Middle Cambrian faunas, for they 

 appear to be less clear-cut than those in the Upper Cambrian forma- 

 tions. This situation no doubt has contributed to the slow develop- 

 ment of Middle Cambrian stratigraphy and to the uncertainty of 

 present correlations. At present it seems that nearly all the common 

 Middle Cambrian genera range throughout most of the division. 

 And further, it seems that one or another genus may undergo great 

 expansion at any time evidently without following a particular 

 evolutionary trend. Moreover, it is apparent that conspicuous ele- 

 ments of several faunas may be present or absent from place to place. 

 In short, at the present stage of knowledge, Middle Cambrian faunas 

 are not clear-cut entities, and their composition varies more than 

 should be expected. This state of affairs can scarcely be attributed 

 to inadequate collection alone, although there is no doubt that further 

 field work will fill in many gaps. 



