CAMBRIAN PLATEAU. 415 



Cambrian rocks. The most striking are perhaps those of the Blacksmith's 

 Fork, which present perpendicular walls nearly 2,000 feet in height, offering 

 fine sections of the limestone. From all the structural observations made 

 in the field, there can be scarcely any doubt but that this great limestone 

 belt represents the Ute formation, already described as resting conformably 

 upon the Cambrian rocks of the west side of the fold, and which here forms 

 the eastern side of a broad anticlinal axis, the strata being inclined at an 

 angle of only 2° or 3° to the eastward. On the summit of the plateau, this 

 limestone is mostly concealed beneath the Tertiar}'- sandstones of the Ver- 

 million Creek beds, or loose, sandy Quaternary soil, and is only exposed 

 here and there in a few isolated localities. No fossils were found in place 

 along the edge of the cliffs, or in the canons, although it may be stated that 

 only a cursory search was made, while a mpre careful examination may 

 show the beds to be as rich in invertebrate remains as the formation on the 

 opposite side of the fold. The thickness of this limestone is estimated as at 

 least 2,000 feet. 



Beaver Canon lies entirely within the Cambrian quartzites. A variety 

 of quartzite exposed here is of some special interest, as it differs from any 

 beds observed in the region of the Muddy and Blacksmith's Canons, but at 

 the same time shows a close lithological resemblance with beds seen at other 

 localities in the Wahsatch Range. It is characterized by purplish-gray color, 

 vitreous lustre, and a tough, dense texture. The individual grains of quartz 

 have a dark, smoky appearance, while the interstices between the grains 

 are filled with crypto-crystalline, almost amorphous, quartz. Many of the 

 beds develop a tendency to a schistose structure, containing interlaminated 

 seams of thin, partially-foliated quartz, between layers of coarser material. 

 Under the microscope may be recognized a few minute plates of mica, while 

 the quartz grains reveal large numbers of liquid-inclusions with mobile bub- 

 bles. These purplish-gray rocks, by the absence of iron, present a marked 

 difference from the white and brown quartzites of the Cambrian series. The 

 recorded dips in the canon are all to the eastward. Some 2 or 3 miles 

 from the head of Beaver -Canon occurs a large deposit of calcareous tufa, 

 formed by an old thermal spring, which has now nearly ceased running. 



