256 Davis — Notes on the Colorado Canyon District. 



states that when the great denudation began, there were no 

 faults and no benches; the first uplift was broad and even, 

 without differential displacements; the displacements began 

 later, and so slowly as not to affect the course of the original 

 streams (1. c, 200, 201). Dutton dates the Hurricane fault as 

 later than the earlier lava flows and earlier than the later ones 

 (hence later than the great denudation and before the later 

 canyon cutting) ; the Toroweap fault was not begun until the 

 upper canyon had attained very nearly its present form, so that 

 the floor of the esplanade as a topographic feature was dislo- 

 cated by the fault; the Kaibab began to have a distinct 

 existence only after the great Miocene denudation, when the 

 Colorado was beginning the erosion of the upper canyon ; the 

 Echo cliffs monocline is rated as very nearly coeval with the 

 East Kaibab monocline, and the latter began with the Pliocene 

 (1. c, 117, 94, 192, 205). Walcott places the uplift of the 

 Kaibab before the completion of the great (Miocene) denuda- 

 tion,* while there were still some heavy overlying strata upon 

 it, because the layers of the monoclines are flexed without 

 manifest fractures. The dating of the displacements there- 

 fore still offers an interesting subject for discussion. 



AVhile subordinate movements on the fault lines and mono- 

 clines may have occurred during the erosion of the inner canyon, 

 the chief movements seem to be much older. This conclusion 

 is enforced by several observations. First, there is the arrange- 

 ment of the Permian and Triassic escarpments with respect to 

 the northern extension of the fault lines : had the faults been 

 of recent date, later than the great denudation by which the 

 escarpments were pushed back for scores of miles from the 

 original extension of their strata, the borders of the several 

 formations as shown on a map ought not to be significantly out 

 of line on the two sides of a displacement; for in the post- 

 displacement period there would not have been time for much 

 retreat of the cliffs on one side of a fault in excess of the 

 retreat on the other side. But as a matter of fact, the Permian 

 and Triassic cliff-makers have been greatly denuded with 

 respect to and subsequent to the displacement of the blocked 

 plateaus. The Permian cliffs retreat northward as they 

 approach the Hurricane fault south of Toquerville ; the Per- 

 mian and the Triassic cliffs are out of line by several miles on 

 the two sides of the fault that passes near Pipe Spring, west of 

 Kanab. This style of arrangement was recognized by Powell, 

 who stated that the higher blocks have been more eroded than 

 the lower ones, and hence " the cliffs of the higher blocks 

 stand further back from the axis of upheaval than those of the 



*Bull. G-eol. Soc. Amer., i, 1890, 60, 64. 



