DAVIS: THE GRAND CANYON OF THE COLORADO. 149 
come flexures near their northern end, as is noted for one of them, 
above, and as is the case with the Hurricane fault proper, just north of 
Virgin river. But the only flexure on the western side of the Kaibab 
mentioned by Dutton is one by which the thrown beds are turned down 
as they approach the fault plane from the west (c, p. 128). 
The northeast dip of the flexure that separates the Coconino plateau 
from the Kaibab is strongly marked. Strong eastward dips are observ- 
able on the lines of the Grand wash fault and of the great fault (almost 
in line with the Hurricane fault) north of Toquerville. The rule that 
the faults throw to the west and that the flexures throw to the east is 
therefore very generally obeyed. 
The frequent association of flexures and faults on the same line is 
noted by several observers. Dutton described the downward flexure of 
the thrown beds in connection with the Hurricane, Sevier, and west 
Kaibab faults (¢, pp. 41, 113, 114, 115, 128, 185, 186) ; while Gilbert 
(a, p. 54) and Marvine (p. 196) give diagrams of the Grand wash fault 
which exhibit the same feature. Dutton suggests that flexing pre- 
ceded faulting (c, p. 115), and Walcott discusses a remarkable pre-Cam- 
brian fault with throw to the west, on the line of which the east Kaibab 
torn flexure was formed in Tertiary time, with throw to the east 
(d, pp. 49-64). It seems probable that the prevailing coincidence of 
flexures and fractures may elsewhere, as well as in the east Kaibab 
example, be associated with faults of ancient origin, possibly in the 
pre-Cambrian foundation of the palzozoic and mesozoic strata, although 
it is only in the Grand canyon that this relation is open to study. 
It is certainly remarkable that the distinct flexures of the Grand 
canyon district dip eastward so generally, while the faults have their 
throw to the west with almost equal regularity. In all cases where this 
relation obtains, the later movement by faulting was of greater measure 
than the earlier movement by flexing. It is further noteworthy that 
the unfaulted or least faulted flexures, such as the Waterpocket, Echo, 
and east Kaibab, lie to the east; while the distinctly faulted flexures 
lie to the west. It may also be remarked that, if the difference of date 
here inferred for flexures and faults holds true, it will be inappropriate 
to use the term “ Kaibab structure ” in the sense given to it by Powell 
(4, pp. 14, 22), and adopted by Gilbert (4, p. 86); namely, as a designa- 
tion for a. plateau that “ primarily” surmounts lower ground on both 
sides. The greater part of the altitude by which the Kaibab surmounts 
the Kanab on the west is probably not a primary feature, but a second- 
ary one, due to faulting after flexing. 
