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the roughly concentric attitude of the escarpment 

 of horizontal Eocene on the northwest with the 

 escarpments of the swell itself (a, pp. 19, 20) ; 

 hut it nevertheless seems permissible to class this 

 dome-like uplift with the "Waterpocket and Esca- 

 lante flexures as having been formed in what ma}' 

 be called the Cretaceous-Tertiary interval, and 

 as having been, like the flexures, greatly eroded 

 before it was buried by Eocene deposition. True, 

 the unconformity thus implied is nowhere pre- 

 served, for the Eocene strata have now receded 

 to a distance of about forty miles from the centre 

 of the swell ; but some indirect evidence for their 

 original unconformable extension over the eroded 

 swell is found in the small amount of adjustment 

 of two transverse streams to the domed struc- 

 tures, as will be more fully stated further on. 



The Kaibab and the Echo (Paria) Flexures have 

 been described as about contemporaneous with 

 the broad uplift that introduced the erosion of 

 the Grand canyon (c, pp. 192, 205), but they seem 

 to be of older origin if one may judge of the date 

 of their deformation by the recession of the Trias- 

 sic cliffs that stand in association with them. This 

 is shown as follows : The Triassic (Vermilion) cliffs 

 have retreated at least twenty-five miles around 

 the northern end of the Kaibab since its uplift- 

 ing ; and the same Triassic cliffs have retreated 

 to close coincidence with the line of the Echo 

 (Paria) flexure since its production, from what- 

 ever irregular line of front they had previously 

 when the strata were horizontal. But, on the 

 other hand, the upper Aubrey cliffs, enclosing the 

 outer gorge of the canyon in the Kanab and Uin- 

 karet plateaus, have retreated only two or three 

 miles since the beginning of the canyon cycle. 

 Surely then the Kaibab arch and the Echo mo- 

 nocline must be older than the beginning of 

 the canyon cycle. Moreover, Walcott has called 

 attention to the flexure of the east Kaibab mono- 



