HINTZE, GEOLOGY OF WASATCH MOUNTAINS, UTAH 97 



be traced southward through the Alta basin at the head of Little Cotton- 

 wood Canyon, into American Fork Canyon/^" At Santaquin, near the 

 Union Chief mine 40 miles to the south, it is seen again, being there 600 

 feet below the top of the series. The black formation on which it rests at 

 the head of Little Cottonwood Canyon seems to be absent everywhere 

 within a few miles to the north and south of that place, not appearing in 

 Big Cottonwood Canyon, nor at Santaquin to the south. From its occur- 

 rence thus traced for about 50 miles, it may safely be taken to be of wide 

 distribution. That it truncates the lower beds, producing extraordinary 

 differences in their thickness within short distances, is also clear from the 

 rapid disappearance of the black member, above referred to, and from the 

 fact that northward at Willard, Utah, the conglomerate rests directly on 

 Archean gneiss. The possibility of original inequality of thickness must 

 be taken into account in connection with the thinning of the lower series. 

 The uniform thickness and wide distribution of the quartzite and shale 

 member overlying this dividing plane, taken together with the great vari- 

 ation in thickness of the lower series, seem to imply the widespread trun- 

 cation of the lower beds and their reduction practically to a peneplain 

 before the upper beds were deposited. The complete removal of the great 

 quartzite series over considerable areas must have required much time. 

 A great gap therefore separates the Lower Cambrian quartzite at the top 

 of the series from the great quartzite and shale series underlying it, and 

 the two must be of distinctly different ages. 



Accepting Walcott's fossil evidence of the presence of Lower Cambrian 

 strata above the unconformity, it seems only proper to regard the quartz- 

 ite-slate series below as of pre-Cambrian, and probably Algonkian age. 

 It would then correspond to the Belt series of Montana and the Grand 

 Canyon series of Arizona, in both of which the Cambrian strata are sepa- 

 rated from the pre-Cambrian formations by similar unconformities. 



A very different view is held by Daly and others, namely, that the oldest 

 Cambrian fossils in the Eocky Mountains are Middle Cambrian and that 

 the Brigham quartzite is of that age. The unconformity is regarded as rep- 

 resenting only a brief time interval, and the great quartzite-slate series is 

 made early Cambrian and not Algonkian in age. This view seems to call 

 into question the faunal evidence upon which the presence of Lower Cam- 

 brian strata at the top of the series is based. Dr. Walcott very kindly 

 supplied the writer with photographs of two specimens of Olenellus gil- 

 herU, which he found at the base of the shale bed, and there seems to be 

 no reason to doubt their correct identification. A diligent search in all 



loa. See Plate I, fig. b. 



