REPORT OF THE DIRECTOR I92O-2I 91 



of the world. From Walcott's excellent description (1895, p. 312) 

 of this section we know that the river has cut into the Archean 

 gneiss which, as everywhere, is intensely folded. Upon this rests 

 unconformably the Algonkian or Proterozoic series, which again 

 in its turn is folded and eroded and overlain by the little tilted 

 Cambrian. Since that time the Colorado plateau has not been 

 folded again. A recent reconnaissance of the Archean complex 

 in the Canyon (Noble & Hunter, 19 17) and a number of folios 

 of the Colorado plateau afford fairly conclusive evidence of the 

 direction of the Precambrian folding there. Noble (p. 113) who 

 did the field work, found that nearly all the Archean rocks were 

 recrystallized and " acquired a gneissoid or schistose banding 

 which has a dominant northeast strike and a nearly vertical dip." 

 It is added that this structure suggests that the compressive forces 

 acted either from the northwest or from the southeast, and that a 

 similar structure has been found to characterize th%Archean complex 

 in the Globe region described by Ransome (1903), and the complex 

 on the west and southwest border of the Grand Canon district 

 described by Schrader (1909). 



The general northeast to north-northeast strike of the Archean, 

 underlying the Colorado plateau, is clearly brought out by a number 

 of folios. 



Ransome (1904, p. 2, 3) in the Globe folio (north of the Gila 

 river and of Tucson) states that the schistose cleavage of the rocks 

 (" Pinal schist," probably equivalent to the Algonkian "Vischnu" 

 series of Walcott in the Grand Canon) which is roughly parallel 

 to the banding, due to differences in composition of the schists, 

 strikes to northeast and thus runs nearly at right angles to the 

 dominant trend of the present mountain ranges of the region. Also 

 the " Schultze granite " forms narrow northeast-southwest intrusions 

 in the schist. The dip is to the northwest. Ransome (1904) 

 found the same condition on the Bisbee quadrangle, which is on 

 the Mexican line, where the dominant trend is north-northeast — 

 south-southwest. On the Clifton quadrangle, 80 miles east of 

 the preceding and near the New Mexico line, Lindgren found 

 the schistosity striking in various directions, and likewise variable 

 indications of stratification in the schists, the outcrops, however, 

 too small and scattered to allow the establishment of the general 

 trend. Wherever the outcrops are large and continuous, as on 

 the Bradshaw quadrangle (Jaggar & Palache, 1905), which lies 

 southeast of Flagstaff in central Arizona, there the Proterozoic 

 (" Algonkian ") schists show a distinct northerly trend, as distinctly 



