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 monoclinal 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 
usual order of progress in which erosion acts in a more retrogressive 
fashion. 
The topographical maps of the Kaibab (Dutton, c, Atlas, sheets XXI., 
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. Near 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; but 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 
