DAVIS : THE GRAND CANYON OF THE COLORADO. 149 



come flexures uear 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 (c, pp. 41, 113, 114, 115, 128, 185, 186) ; while Gilbert 

 (or, 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 palaeozoic 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 

 (b, pp. 14, 22), and adopted by Gilbert (b, 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. 



