202 
THE GEAND CAS^OI^ DISTEICT. 
In the case of the ravines of the Kaibab we saw some reason to con- 
jecture that they had their origin during the glacial period. So, too, with 
the surface channels of the Paria Plateau the same conjecture seems appli- 
cable. In this region the glacial period was not icy. No traces of glacial 
action are discernible in the country round about until we reach the loftier 
heights of the High Plateaus — 9,000 to 11,000 feet above the sea. But 
there is reason to believe that glacial time is here represented by a rainy 
period coming in between the arid climate of the Pliocene and the arid 
climate of the Quaternary. In truth the evidence of this is decisive. It 
is therefore natural for us to look for just such traces of its former pres- 
ence as this network of canons, or as the ravines of the Kaibab. For the 
effect of a long-continued arid climate is to obliterate the smaller streams, 
to increase the areas, and diminish the number of subordinate watersheds. 
The return of a moist climate would revive the minor channels. But if 
the arid climate had prevailed for a long period, and if during its sway the 
country had undergone differential vertical movements, the revived chan- 
nels would not necessarily occupy the precise places of their predecessors. 
That would depend upon how deeply the original channels had been 
engraved, how extensive or nearly complete had been their obliteration, 
and how strongly marked had been the intervening vertical movements. 
On the Kaibab and Paria plateaus these factors appear to have had such 
values that the moist climate of the glacial period gave rise to networks of 
channels, which were quite independent of any which may have existed 
there in the Miocene. 
On the Paria Plateau not a solitary channel carries a living stream 
except the Paria River, which receives its supply of water from the much 
loftier and moister region of the High Plateaus far to the northward. The 
extinct channels flow into it, and have directions which are very plainly 
determined by the general dip of the Paria table, which is towards the 
northeast. 
Wherever we turn in the Plateau Country the drainage is constantly 
bringing up many interesting problems and suggestions, and happily also 
supplies answers more or less complete to many questions. I do not know 
of any other region where this subject is so fruitful or so entertaining’. The 
