

6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



ABSENCE OF LOWER CAMBRIAN 



Lower Cambrian strata are apparently absent in the Wasatch 

 Mountains northward of Salt Lake City. At the southern end of the 

 range near Mount Nebo, in Cottonwood Canyon, south of Salt Lake 

 City, and on Promontory Point in Great Salt Lake, about 20 miles 

 west of the Wasatch Mountains, fossils show that the Lower Cambrian 

 seas extended northeastward from southern California and Nevada 

 at least as far as the mentioned points. Wherever the base of the 

 Cambrian beds is exposed north of Salt Lake City, the Brigham 

 quartzite is seen to rest directly on pre-Cambrian rocks. The situation 

 obtains also in the Salt River and Teton Ranges of western Wyoming, 

 in the northwestern part of Yellowstone Park, and throughout 

 Montana. In my opinion the Lower Cambrian rocks found in the 

 vicinity of Great Salt Lake possibly continue beneath younger strata 

 and the lava fields, to connect with outcrops in northeastern Wash- 

 ington and beyond that with beds of similar age in the Columbia 

 Valley and Dogtooth Mountains of British Columbia. Since Lower 

 Cambrian strata are clearly absent in the northern Wasatch region, 

 and thence northward through western Wyoming and Montana, the 

 question arises whether the lowest Cambrian beds exposed are the 

 oldest Middle Cambrian, or whether some Middle Cambrian also is 

 lacking. 



MIDDLE CAMBRIAN FORMATIONS 



The three independent measurements combined with the fact of 

 excellent exposure of a complete sequence results in Blacksmith Fork 

 becoming the basic section of the area. All other sections that have 

 been investigated agree closely, with the exception to be subse- 

 quently noted. Six formations evidently constitute the Middle Cam- 

 brian sequence for the northern Wasatch region. A condensed table 

 is presented for ready reference. 



In the Blacksmith Fork section the figures in parenthesis are 

 Deiss' measurements ; those in brackets are Blackwelder's. The 

 Randolph quadrangle section is composite but is based primarily on 

 the exposures immediately northeast of Garden City. The figures for 

 Two Mile Canyon may not be wholly reliable, since accurate adjust- 

 ment may not have been made for all the faults that interrupt the 

 section. While the sequence exposed near the crest of the range north 

 of Brigham is evidently the same as at Two Mile Canyon, Walcott's 

 notes are insufficient to warrant inclusion of a column in the table. 



