ABSTEACT OF THE MONOGRAPH. 
5 
Toroweap Valley is also inferred. It appears to be the channel of an an- 
cient river long since dried up. It is the type of a number of ancient trib- 
utaries of the Colorado, which collectively throw light upon its Tertiary 
history. Many other facts are recited, for which the reader is referred to 
the chapter itself 
Chapter VI describes the Uinkaret Plateau. Since the Uinkaret and 
Sheavwits are very similar to each other in their geological features and 
relations, the former alone is discussed as the type of the two. Three sub- 
jects receive attention: 1st, the volcanism ; 2d, the Hurricane fault; 3d, 
the remnants of Permian strata. The lavas are all basaltic and very homo- 
genous in character. They are of two ages, the earlier being referred 
approximately to the early Pliocene or possibly late Miocene, the later to 
very recent time, some being probably but a very few centuries old. A 
long interval of time separated the two eruptive periods. 
The Hurricane fault is al'o described at length, and its comparative 
recency pointed out. The Permian remnants here are important as relics 
of an ancient topography preserved by the protection of the more ancient 
basalts, and as indicating the former extension of that formation over the 
entire district. The lavas, the fault, and the Permian all throw light on 
the sequence, epochs and relations, of those events which make up the his- 
tory of the region. Each by itself would be of little moment. But by 
grouping them together in their proper relations and viewing them as a 
whole they reveal much. It now begins to appear that the chasm had its 
origin in the latter part of Tertiary time, that the faults are no older, and 
that they, as well as the volcanism of the region, are associated with periods 
of upheaval, and that these periods are reflected in the various stages of the 
excavation of the chasm. The great denudation also finds further support 
in the facts here presented. 
Chapter VII resumes the narrative treatment, and the reader is con- 
ducted on an imaginary journey from the base of the Vermilion Clifis to 
the Kaibab Plateau and upon its summit to the brink of the chasm. Along 
the route such facts as are of special geological interest are noted and 
remarked upon, and the attempt is made to convey a mental picture of the 
region traversed. I have taken the liberty in this chapter of attacking the 
