DAVIS : THE GRAND CANYON OF THE COLORADO. 157 



east and west as to allow their infacing escarpments to shed water into 

 the lateral subsequent valleys opened on weak inonoclinal strata along 

 the flanks of the uplift. But when a sufficient retreat of the Trias had 

 been accomplished and the lateral subsequents had been developed, the 

 axial or anticlinal streams would be reduced to small volume ; for 

 much of the drainage of the uplift that used to enter them will at this 

 later stage flow away from them down the stripped structural slopes on 

 either side. The drainage of the stripped slopes forms a new series of 

 lateral waterways ; they are not strictly consequent streams which have 

 persisted since the Kaibab was uplifted, but are regenerated successors 

 of the original consequents. It may be noted that the valleys of such 

 regenerated consequent streams will have been eroded first in their 

 upper parts and afterwards in their lower parts, thus reversing the 

 iisual order of progress in which erosion acts in a more retrogressive 

 fashion. 



The topographical maps of the Kaibab (Dutton, c, Atlas, sheets XXL, 

 XXII.) allow us to compare these deduced conditions with the facts. 

 The lateral subsequent valleys have now shifted to the lower ground 

 bordering the Kaibab, by reason of the far and wide retreat of the 

 Trias ; the most representative example being House-rock valley, well 

 enclosed by the Trias of the Paria plateau which still stands near the 

 Kaibab on account of the relatively low level of the Marble plat- 

 form. The regenerated consequents have scored the flanks of the 

 plateau with deep ravines. Four axial valleys all discharge eastward 

 from near their northern ends. Xear the northern termination of the 

 Kaibab Carboniferous area, there is a canyon that cuts directly across 

 the uplift, draining a portion of the western Permian monoclinal valley 

 to the corresponding eastern monoclinal valley (House-rock valley) at 

 Adairville ; this probably being an example of structural superposition, 

 that is, of a stream whose course was determined when the weak over- 

 lying Permian strata still covered the area during the plateau cycle 

 and whose course has been maintained through the resistant Carboni- 

 ferous strata. The only exception to the rule of eastern discharge is 

 in the case of the southern end of De Motte valley ; bat this lies 

 beyond the area of greatest altitude on the Kaibab (nine thousand feet) 

 and discharges, as might have been expected, southward to the canyon. 

 It is therefore not necessary to conclude that the "Summit valley" 

 depressions of the Kaibab were ever drained by a single antecedent 

 stream, and it seems advisable to regard the Kaibab uplift as having 

 taken place long before the mesozoic strata were stripped from its 



