694 ^y. j. miller — pre-cambrian folding in north America 



ARIZONA AND NEW MEXICO 



In the Shiimmo Quadrangle (Noble, 1914) of the Grand Canyon dis- 

 trict steep-dipping Archean schists exhibit a general northeast strike, 

 with local variations. Tilted and faulted, but not folded, Algonkian 

 strata rest on the schists. 



The Bradshaw Mountains of central Arizona (Jaggar and Palache, 

 1905) contain pre-Cambrian rocks which were highly folded, with a gen- 

 eral north-south strike, before Paleozoic time. 



The Globe district (Ransome, 1904) shows an extensive development 

 of steep-dipping pre-Cambrian schist with a northeast strike. Eansome 

 says : 



"It is noteworthy that the strike of the schistose cleavage runs nearly at 

 right angles to the dominant trend of the present mountain ranges of the 

 region." 



Much faulted, but little folded. Paleozoic strata rest on the schists. 



A small area of steep-dipping pre-Cambrian schist and granite in the 

 Clifton, Arizona, region (Lindgren, 1905) shows varying strikes, rang- 

 ing mostly between east-west and north 30 degrees east. 



The Bisbee area (Ransome, 1904), in the southeastern corner of Ari- 

 zona, contains steep-dipping pre-Cambrian schists with a dominant strike 

 about north 25 degrees east. Only moderately folded Paleozoic strata 

 rest on the schists. 



But little information regarding pre-Cambrian structures in New Mex- 

 ico seems to be available. In the northern part of the State there are 

 several belts of pre-Cambrian rocks, but their north-south trend does not 

 necessarily indicate such a pre-Cambrian structural trend. Thus, in re- 

 gard to the schists and granite of the Cimarron belt Stevenson (1881) 

 says that "the dips of the Archean rocks are much confused." 



For the most part, then, in Arizona and New Mexico, the definitely 

 known pre-Cambrian structural trend-lines make high angles not only 

 with the trend-lines as shown on Ruedemann's map, but also with the 

 general trend of the Rocky Mountains. 



NEVADA AND UTAH 



Few reliable observations on pre-Cambrian structures appear to be 

 available for Nevada, where definitely known pre-Cambrian rocks are not 

 extensively developed. The West Humboldt Range (Emmons and Hague, 

 1877) shows steep-dipping schists and gneisses with strike north 38 de- 

 grees east. 



The Snake Range of eastern Nevada (Weeks, 1907) contains steep to 

 moderately steep dipping quartzite with a west-northwest strike. 



