56 



D. WALCOTT — A DISPLAt EMENT IN THE GRAND < \\"\. 



1,200 to 1,500 feet Upon this data the restored outline of the pre-Tonto 

 position of the strata, prior to the Tertiary displacement :it the crossing of 

 tion v . is given in section 9. The west branch of the limit is inclined :)(>' 



West. 



East. 



T.Sd. 



/,. .i-.. - -— r 



■■ I-"- '" I- 





: 



G.C. 



P.T. 



Figubi '.'. — A Restoration of Section 8. 



ting the block forming Chuar lava hill before the Tertiary faulting and erosion of Chuar 

 valley and the Grand ' iafion. The lettering i* the same aa in ~<-<-t i. .ti g. 



from the vertical to the west, and the cast branch is nearly vertical : a fact 

 that serves to explain the Tertiary movement following the latter, as it was 

 mainly a vertical displacement. 



'/'//< pre- Cambrian Movement. — The westward throw of the pre-Cambrian 

 AJgonkian) fault, varied at differenl points from tOO to 4,000 feet, owing to 

 its traversing strata that dip both with and against its strike. All along its 

 line, except in Nun-ko-weap and Chuar valley- and across the Colorado 

 opposite Clinar valley, the strata on the eastern Bide are now concealed by 

 the carrying down of t he Tonto and superjacent rocks by the Ten iary move- 

 ment. In sections 1 . '_', - s , and 9 the pre-Tonto strata an' shown on each side 

 of the fault, and on the east Bide of Chuar valley the beds of the Chuar 

 group are -'en lying up against the west side of the lava hills, mi the line of 

 the oblique western branch of the fault I fig. s i. To the Bouth the fault pa-- - 

 through a -addle eroded through the Tonto sand-tone between the hill south 



of Chuar lava hill and the main ridge. This proves that the fault crossing 



the saddle, with a throw of from 1,200 i" 1,500 feet, is of pre-Cambrian 

 , as the line nf the Tonto sandstone ha- been scarcely more than 

 broken by the slight reverei movement that occurred during Tertiary time 

 on the main fault and it- eastern branch. In every instance where strata of 

 the (huar group approach the fault the beds are flexed up toward- it on a 

 tad Bcale, ;i- shown in Bectione I. •». ii. 7, ami 8. Bach from the displace- 

 ment this flexure disappears by the decrease of dip, as shown in section i, 

 when- the beds are horizontal one half mile hack of the fault, or in Bection 

 6, w her. a synclinal in tonne! l. The general dip of the pre-Tonto beds is to 

 tie northeast. South of (huar valley, beyond where the faull disappears, 

 tin- strike of the strata i- regularly to the northwest and southeast. 



A - determined from the section of the pre-t iambrian fault exposed to ex- 



