252. BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
field for a summer’s geological study. Not only are there most interest- 
ing problems to be worked out, but there is the finest of scenery and a 
delightfully cool invigorating climate, utterly different from the sultry 
desert of the lower plateaus and valleys. 
The Post-Fault or Canyon Cycle of Erosion. 
The Normans relate an Indian tradition that long ago there was 
snow all the year round on the Pine Valley mountains, although it does 
not now come until November and is gone in June. Also, the valley 
of Ash creek was smoother than now and had no canyon: a great flood 
came and washed it out. Whether these are pure Indian traditions or 
an adaptation of the remarks of some early white explorer, we could not 
ascertain. If it is the former it is highly significant, and even if it is 
the latter it is essentially true, though less interesting. The canyon 
cycle must include at least the latter part of the glacial epoch, although 
no traces of glaciation have been noticed in our immediate district. It 
certainly has witnessed the change from the relatively smooth topog- 
raphy of the inter-fault cycle to the rough topography of the present. 
How much of this change occurred after man appeared on the earth 
has not been determined, but erosion proceeds so rapidly in this naked 
country that it is quite possible that a considerable portion of the work 
of the last cycle has been done since the first human inhabitants settled 
here. 
The work of the Canyon cycle has consisted chiefly of the removing 
of weak strata that were formerly below sea-level, the cutting of deep 
canyons, and the steepening and renewal of cliffs. All these features 
are illustrated in the accompanying diagrams (Fig. 12), in which I 
represents the conditions previous to faulting, and JZ those of the 
present. In the first sketch, the Carboniferous series, A, and the over- 
lying Moencopie shales, 6, had been reduced to a peneplain, the surface 
of which is shown by the line HJ, and on this had been ejected a lava 
flow, G. Farther north the same soft shales were protected by the hard 
Shinarump, C, with the result that there was a long gentle slope from 
the peneplain upward. Among the higher strata the soft Painted Desert 
series, D, and the hard Kanab sandstone, /, formed another slope of 
equally gentle ascent rising to the upland, /, of Colob and Cretaceous 
strata. At H and J were two rivers flowing toward the west in insig- 
nificant valleys. When the country was uplifted to the position which it 
now occupies, rapid changes began, which up to the present have gone 
