526 E. BLACKWELDER GEOLOGY OP WASATCH MOUNTAINS, UTAH 



part of the Belt and Grand Canyon terranes^ basing his interpretation on 

 their physical characteristics. If all of these formations were in fact 

 deposited chiefly by rivers on extensive plains in a climate which was 

 semi-arid, or at least subject to dry seasons, it becomes much easier to 

 explain the great scarcity of fossils throughout all of these essentially 

 unaltered sediments, and also accounts for the fact that the few fossils 

 which have been found are apparently Discinoids and Eurypterids, such 

 as are commonly found in younger rocks not of strictly marine origin. 



THE OGDEN QUARTZITE ELIMINATED 



In Ogden Canyon two thick beds of quartzite appear to be separated 

 by several hundred feet of shale and limestone. The geologists of the 

 Survey of the 40th Parallel considered the lower of these to be Cambrian. 

 The upper formation was named the "Ogden quartzite," and its age was 

 thought to be approximately Devonian. This classification stood un- 

 challenged for more than a generation. A few years ago Weeks^^ found 

 Ordovician fossils in a quartzite and shale formation north of Brigham. 

 This quartzite was separated from the Cambrian quartzite by a thick 

 series of shale and limestone, and on this account Weeks considered it the 

 equivalent of the "Ogden quartzite." 



Contrary to this early view, the "Ogden quartzite" in Ogden Canyon 

 is now believed to be merely a slab of the Cambrian quartzite repeated in 

 this place by an overthrust. It is in fact twice repeated, but an ob- 

 server traversing only the bottom of the canyon would see only a single 

 repetition, as indicated in the structure section (see figure 6). The 

 existence of these overthrusts is demonstrable, and the proof rests on 

 more than one kind of evidence. From the rim of the canyon, either 

 north or south, the structure can be seen as plainly as in a diagram (see 

 plate 39, figure 1. The beds beneath the overthrust are much con- 

 torted, and the succession above the "Ogden quartzite" is identical with 

 the succession above the Cambrian quartzite. A careful search even 

 revealed Middle Cambrian fossils characteristic of Walcott's Pioche shale 

 just above each of the three layers of quartzite in the canyon. Finally, 

 the overthrusts which are responsible for these repetitions were traced 

 horizontally 10 to 20 miles. They cut diagonally across the formations 

 beneath and in details give ample additional proof of the structural con- 

 ditions described. 



In this connection it is well to note that an early Paleozoic quartzite 

 formerly correlated with the "Ogden quartzite" is widely distributed in 



18 F. B. Weeks : Unpublished report to the U. S. Geological Survey, 1908. 



