520 E. BLACKWELDER — GEOLOGY OF WASATCH MOUNTAINS, UTAH 



recent normal faulting and topographic development, and by Atwood^^ 

 on the glacial features. Mention is not made in this list of numerous 

 smaller contributions, all of which have had their value. 



In the following pages the writer presents some additional information 

 about Wasatch geology. It is to be hoped that so interesting and im- 

 portant a region will not long await the thorough study which it deserves. 



SEPARATION OF CAMBRIAN FROM ALGONKIAN 



The earlier explorations of the Wasatch range revealed beneath the 

 oldest fossiliferous rocks a great series of quartzites and slates, having an 

 estimated thickness of 12,000 feet. Walcott found the Olenellus fauna 

 at the top of this succession, near Salt Lake City, and recommended that 

 the great quartzite series should be placed in the Algonkian system, since 

 it lay beneath the Olenellus horizon. The series is best exposed in Big 

 Cottonwood Canyon, south of Salt Lake City, but it appears also in a 

 line of low mountains which extend from the upper canyon of Ogden 

 Eiver northwest to the town of Brigham. 



Up to 1909 no line of division had been found between the fossiliferous 

 part of the Cambrian and the great mass of the quartzite-slate series. 

 The geologists of the Survey of the 40th Parallel considered the entire 

 succession conformable, and therefore called it all Cambrian. Walcott 

 also regarded it as conformable, but applied the name Algonkian to the 

 barren downward extension of the lower Cambrian. Two facts, however, 

 suggest the existence of an unconformity within the quartzitic series: (1) 

 The quartzite shows remarkable variations in thickness. Although 12,000 

 feet thick in Big Cottonwood Canyon, it is less than 1,500 feet thick at 

 Ogden, is at least 10,000 feet thick northeast of Huntsville, is again 1,000 

 to 1,500 feet thick at Willard, and is several thousand feet thick at Brig- 

 ham. These great fluctuations within short distances seem to demand a 

 special explanation. (2) The conglomerate bands, of which there are 

 many in the upper part of the quartzite series, contain more pebbles of 

 quartzite than of all other rocks combined, and many of these quartzite 

 pebbles bear a strong lithological resemblance to the bright-colored 

 quartzites farther down in the supposed Algonkian. 



The writer was not so fortunate, however, as to find the unconformity 

 exposed until, at the close of the season, he visited Big Cottonwood Can- 

 yon. There, at a horizon roughly estimated about 1,500 feet beneath 

 the top of the quartzite, a well marked conglomerate is exposed. It is 



13 W. W. Atwood : Glaciation in the Uinta and Wasatch Mountains. U. S. Geological 

 Survey, Professional Paper 61, 1909. 



