NO. 24 PTARMIGANIA STRATA RESSER I J 



Langston. Nothing is recorded concerning the sedimentation of the 

 beds, consequently unconformities, if present, have been overlooked. 

 But with the lithologic and stratigraphic evidence in hand, it is pos- 

 sible to say that the Ptarmigania beds can be Langston equivalents. 

 So if the Ptarmigania beds are not the Langston formation it must be 

 proven solely by faunal evidence. 



The composition and age of the Ptarmigania fauna are discussed 

 later. Comparing that fauna with two collections in unquestioned 

 Langston limestone, . we see that they are not identical but closely 

 related. Certainly they are not mutually exclusive. Without doubt 

 the Ptarmigania fauna is very closely allied to that in the top of the 

 Brigham formation on Mill Creek. Also it is closely allied with 

 the Spence shale fauna. In other words it is not possible on faunal 

 grounds to postulate a large gap in the Liberty section between the 

 quartzite and the Spence shale. 



The nearest relationships of the Ptarmigania to described faunas 

 is to the Albertella fauna. If Albertella and Vanuxemella are removed 

 from the typical Albertella fauna, the remaining genera are nearly all 

 the same. Kootenia expands greatly and the Lower Cambrian ele- 

 ments such as Poulscnia and Prosacanthoides remain, so that the 

 Ptarmigania fauna appears to belong in the early Middle Cambrian, 

 possibly exactly equivalent to the Comet shale of Nevada. 



To sum up, we can only say that the evidence in hand supports both 

 interpretations, namely, that the Ptarmigania beds represent the 

 Langston formation, or that the Langston is absent and these beds are 

 bioherms in the basal Ute or top of the Brigham formation. 3 



COMPOSITION OF THE PTARMIGANIA FAUNA 



Most of the species described in this paper come from the 6-foot 

 limestone bed in Two Mile Canyon (loc. 54s), and they constitute 

 the Ptarmigania fauna. It then remains to determine which other lots 

 of fossils are exactly the same. Of the fossils herein described only 

 those from the 30-foot limestone in the Mill Creek section (Iocs. 59c, 

 59,f, 19s) are regarded as precise equivalents. 



An effort has been made to determine faunules within the 

 Ptarmigania fauna. Two are recognizable, but there is not much 

 difference between them. All species are not indiscriminately mixed 

 in any one piece of rock, but when association of species in many 



2 In his recent letter Prof. Deiss reports finding Albertella in Two Mile 

 Canyon in May 1939. This substantiates the above argument. 



