OBSERVED STRIKES OF PRE-CAMBRIAN FOLDING AND FOLIATION 695 



Pre-Cambrian rocks are not extensively exposed in Utah, and satis- 

 factory structural data are scarce. In Big Cottonwood Canyon (Em- 

 mons, 1877) of the Wasatch Mountains near Ogden, pre-Cambrian 

 quartzites and schists, with rather high dips, strike northeast, and in 

 Little Cottonwood Canyon schists strike northwest. In the small Farm- 

 ington (Hague, 1877) area of the same general region, pre-Cambrian 

 rocks strike about north-south. 



According to Blackwelder (1910), a considerable body of Algonkian 

 strata lies within the Wasatch Mountains east of Ogden, but structural 

 lines within it are not reported. 



The main body of rock in the midst of the Uinta Eange is late pre- 

 Cambrian quartzite only very moderately disturbed and with a general 

 east-west strike of post-Cambrian origin. 



It is, therefore, clear that the few pre-Cambrian structure lines above 

 recorded from Nevada and Utah show widely varying strikes, mostly 

 notably divergent from Ruedemann's trend-lines. 



COLORADO 



This State furnishes an unusual number of records of pre-Cambrian 

 structure lines from both large and small areas. 



In the vicinity of Silver Cliif (Cross, 1896) pre-Cambrian gneisses 

 strike northeast. 



Small areas of pre-Cambrian (Archean?) schists near Pueblo Gilbert, 

 1897) show strikes varying from north-south to northwest, with little 

 disturbed Cretaceous strata resting on them. 



In the Rico Quadrangle (Cross and Ransome, 1905) a small area of 

 pre-Cambrian schist with steep dips strikes east-west, while within a few 

 miles of it folded Algonkian strata show strikes varying from north 10 

 to 30 degrees east, with scarcely folded Paleozoic strata on them. 



Both Archean and Algonkian rocks are well represented in the Needle 

 Mountains Quadrangle (Cross and Howe, 1905), the general strike of 

 the former swinging from a little east of north to nearly east-west, while 

 the latter (Algonkian) ranges in strike from east-west to west-northwest. 

 Both sets of rocks were notably folded before the opening of the Paleozoic. 



Steep-dipping Algonkian strata in the Ouray Quadrangle (Cross and 

 Howe, 1907) show an average east-west strike, but part or all of this 

 deformation belongs to post- Cambrian time. 



In the Telluride Quadrangle (Cross, 1899) a small area of rather 

 steep-dipping Algonkian strata exhibits a well preserved strike north 65 

 degrees west. 



