The Fault and the Periods of Faulting. 



Description of the Butte Fault. — On the north, near the foot of the high 

 walls in the lower end of Nun-ko-weap valley,* a hill formed of several flows 

 of greenstone, contemporaneous with the deposition of the sandstone inter- 

 bedded with the flows, is capped by a rough, massive, maguesian limestone 

 (fig. 1). The pre-Cambrian Chuar strata dip away from it on the north and 

 west, aud an east and west section shows that the hill is a mass of strata dis- 

 placed, in relation to the beds on the west of it, nearly 2,500 feet, the fault- 

 line c (also e of figure 2) separating them sloping to the west with the 

 down-throw. The eastern side of the hill is cut by two faults, a and b of fig. 

 1. The western fault c is sub-parallel to b, and brings to view the strata 

 that underlie the lava beds of the main portion of the hill. The eastern 

 (Tertiary) fault a has dropped the Chuar and Grand Canon rocks on the 

 east out of sight and brought the Cambrian Tonto sandstone down so as to 

 form the eastern base of the hill. The sandstone beds are vertical, owing to 

 the drag on the eastern side of the fault. 



West. 



East 



Figure 1.— East and West Section at the loiver end of Nun-ko-weap Valley on the North side of the 



Brook. 



R. W. = Red Wall limestone (Carboniferous) ; U. T. = Upper Tonto (Upper Cambrian); T. 

 Sd.= Tonto sandstones (Middle Cambrian?); C=Shales of the Chuar group (Algonkian) ; G. C. = 

 Shaly sandstones of the Grand Canon group (Algonkian) that belong below the lava beds L; a, a 

 = Butte fault ; 6, b and c, c = Pre-Cambrian faults. Vertical scale, 1000 feet = 1 inch. 



West. 



East. 



T. Sd 



C. (c) li. (b) G.C. 



Figure 2.— Section on the North side of Nun-ko-weap Valley. 



The lettering is the same as in fig. 1. The faults c and 6 are here seen only at the surface, but 

 their connection with c and b of section 1 can be readily traced. The 700 feet of the Tonto group 

 above the sandstone and the Carboniferous Red Wall and Aubrey groups are not represented in 

 the drawn section, although occurring above the Tonto sandstone where the section was taken. 



* Nun-ko-weap valley heads as a canon on the east face of the Kaibab plateau, then widens out to 

 a mile in breadth before contracting to its canon outlet leading into the channel of the Colorado 

 river. Its entire length is three miles. See maps accompanying Button's Tertiary History of the 

 Grand Canon, 1882. ._,. 



(ol) 



