106 



INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



K 12. IDAHO AND TTTAH. 



Walcott^®^^ has recently classified the Cambrian oif northeastern Utah and 

 southern Idaho. The localities lie in the vicinity of Logan, between Great Salt 

 Lake and Bear Lake. The classification below is taken from his paper : 



Cambrian formations in northeastern Utah and southern Idaho. 



In a recent paper Blackwelder**'' writes as foUows regarding the Cambrian 

 of northeastern Utah : 



Just below the fossiliferous Cambrian shales and limestones there is a quartzite 1,000 to 

 1,500 feet thick. This quartzite rests now on the eroded surface of the Algonkian quartzite and 

 slate, and now on the much older gneiss and scMst which are generally referred to the Archean. 

 Walcott has named it the Brigham quartzite, but it may be seen most clearly at places such as 

 Ogden and WUlard, rather than at Brigham. The oldest fossils found in the shales are referred 

 by Walcott to the 'Lower Cambrian. The Brigham quartzite may therefore be assigned also to 

 the early Cambrian and the quartzites and slates beneath the unconformity to the Algonkian. 

 There is, however, an alternative view, advocated by Daly and others, that the oldest Cambrian 

 faunas in the Rocky Mountains are Middle Cambrian and that the thin Brigham quartzite is 

 the same in age; that the imconformity represents a brief time interval and that the great 

 quartzite slate series is not Algonkian, but simply early Cambrian. Critical studies o^er a wide 

 area are a necessary preliminary to the settlement of this question. It is to be remembered 

 that the unconformity seems to imply the complete removal of the great quartzite series during 

 the erosion interval and over wide areas. The time involved should therefore be more than a 

 brief interruption. 



The House Range, which lies near the western boundary of Utah, between the 

 39th and 40th parallels, comprises a section which according to Walcott, " extends 

 from well down in the Lower Cambrian to the base of the Ordovician, and is the 

 best and most complete of the Basin Range sections so far studied." 



