226 
THE GEAND CaSON DISTRICT. 
I have in the preceding chapters shown that we find at this epoch the 
first indications of the existence of the great faults. It does not appear, 
however, that these faults all originated at exactly the same epoch, and it is 
certain that their respective amounts of displacement have increased very 
slowly and gi-adually with the lapse of time. Again, we cannot be sure 
that all parts of one and the same fault were begun at the same epoch. 
Indeed, the evidence is overwhelming that the development of these dislo- 
cations has been a very slow and gradual process, and all that can be said 
concerning their condition in the particular epoch of which we are treating 
(close of the Miocene) is that they first betray their existence at that time. 
Before this epoch we know nothing of them ; and at the time in question 
they were of inconsiderable dimensions for the most part. Their formation 
seems to have been incidental to the uplifting of the platform which took 
place about the time the present Glrand Canon began to cut. But concern- 
ing the nature of this association it is useless to speculate. In all the range 
of geological phenomena I know of none more perplexing than a great 
fault, and until we have some semblance of a working hypothesis which 
may serve or help to explain them, it is useless to speculate upon the causes 
of particular cases. 
We may also note the coincidence of the earlier basaltic eruptions 
with this period of uplifting and faulting. It has been noted as a fact of 
very general application, that volcanism is active during periods of upheaval, 
and becomes quiescent during subsidence. Tbe relations of the two classes 
of phenomena in the Grand Canon district appear to conform to the general 
rule. 
The amount of upheaval which took place at the epoch in question 
may also be roughly estimated. It varies from 2,000 to 3,000 feet. The 
uplifting forces then suspended operations for a time, and the drainage 
system sought a new base-level. During this paroxysm of upheaval the 
outer chasm of the Grand Canon was cut; the river corrading down to the 
level of the esplanade in the Kanab and Uinkaret divisions, but below that 
horizon in the Kaibab. The corrasion was probably done as rapidly as 
the country rose, or very nearly so. At first we may presume that only a 
narrow gorge was cut — like the upper portion of the Marble Canon. But 
