122 ANNALS NEW YORK ACADEMY OF SCIENCES 



widespread unconformity between the Pennsylvanian and Mississippian 

 throughout Colorado, Wyoming, northern Arizona and all of Utah, with 

 variable amounts of the Mississippian strata present in the different sec- 

 tions, may explain the absence of the Upper Mississippian strata in 

 Blackwelder's northern sections. That this was a long period of erosion 

 has already been explained, and the disappearance of the Weber north- 

 ward may well be by natural thinning due to overlap. The position of 

 the Weber quartzite in the Oquirrh Mountains above the intercalated 

 beds, which are not represented in the Wasatch sections and those farther 

 to the east, indicates that the hiatus at the base of the Morgan formation 

 in Weber Canyon represents a considerable interval of time. The Mor- 

 gan formation is considered to be of verv' local extent and may be taken 

 to be a part of the Weber. 



The relation of the Weber to the overlying Park City formation is de- 

 scribed in the early reports as one of complete conformity. In the Big 

 Cottonwood section, the division line is covered in most places and was 

 not studied in detail by the writer. The section given by BoutwelP^ in 

 the report on the Park City district, as the type section for that area, 

 was measured in Big Cottonwood Canyon, on the ridge east of Mule 

 Hollow. This section was verified by the writer and may be taken as 

 representative for the upper divisions of the Weber quartzite and higher 

 formations. Of the contact in question, the Park City report reads as 

 follows : 



"No unconformity was obseiwed with the underlying Weber quartzite, or the 

 overlying shale, or within the formation (Park City). Accordingly, it would 

 seem that sedimentation proceeded unbroken from Mississippian time through 

 that part of Pennsylvanian which is represented by the Park City formation." 



Blackwelder^^ on the other hand concludes from his studies in Weber 

 Canyon that there is an unconformity. He says : 



"The Weber quartzite is limited above by an irregular eroded surface, which 

 is not exactly parallel to the bedding ; it was subject to disintegration ; and not 

 merely one, but a variety of beds in the formation were exposed, as is shown 

 by the large amount of chert as well as quartzite in the breccia. On the whole, 

 the evidence for the existence of an unconformity at this horizon seems to be 

 conclusive. 



"The importance of the unconformity is uncertain. If the Weber quartzite is 

 a formation of only local extent, and if some of the more calcareous beds 

 farther north were deposited contemporaneously, then the observed uncon- 

 formity may in fact be due to a slight erosion of the surface of the formation 



^ Op. cit., p. 51. 

 ^Op. cit., p. 533. 



