PALEOZOIC HISTORY. 
207 
wliich will require much study to solve, and their solutions promise to he 
extremely difficult. Within the boundaries of the province exposures of 
rocks older than the middle Carbonifei’ous are very few and far between 
Those which have received attention hitherto are confined to the Uinta 
Mountains and the lowest deeps of the Grand Canon. Limiting our atten- 
tion to the latter region, we find beneath that system of strata which we 
Iiave thus far treated as Carboniferous a great variety of beds which range 
in age from the Archaean to the Devonian. Tln’oughout the Kaibab and 
Sheavwits divisions we find the so-called Carboniferous resting sometimes 
upon highly metamorphic schists of undoubted Archaean age, sometimes 
upon the eroded edges of strata which have yielded Cambro-Sihirian and 
Silurian fossils. In a single instance in Kanab Canon Mr. Walcott found 
in a similar situation a very limited exposure of beds bearing fossils of 
Devonian age. In general, the rocks classed as Carboniferous rest upon 
the Archaean, while the older Paleozoic beds come in only at intervals. 
The contact is always unconformable and usually in a high degree. The 
horizontal Carboniferous beds appear to have been laid down upon the sur- 
face of a country which had been enormously eroded and afterwards sub- 
merged. In the Grand Canon this single fact is indicated to us throughout 
the length of a long, narrow, and tortuous cut thousands of feet in depth. 
But if we pass westward or southward, beyond the limits of the great Car- 
boniferous mass, we find a vast region where a similar state of facts is pre- 
sented. The Sierra country of central and western Arizona, of Nevada, 
and western Utah shows remnants of the Carboniferous resting with great 
unconformity upon older Paleozoic rocks and upon the Archaean. 
In the chapter on the Kaibab (Chap. IX, PI. XXXV) I have spoken 
of the great unconformity displayed at the head of the Grand Canon. 
Probably there is no instance to be found in the world where an uncon- 
formity is revealed upon such a magnificent scale, and certainly none amid 
such impressive surroundings. It is all the more suggestive because it is 
the type and symbol of a great fact which prevails over a region large 
enough for an empire. It assures us that in early Silurian time this region 
received enormous deposits of detritus which were faulted and flexed; that 
they were afterwards raised above the waters with the accompaniment of 
