THE BOTTOM OP THE CANON. 
97 
fragments. It is clear that during the epoch of eruption a lateral valley had 
been excavated there ; otherwise, the tufa could not be resting upon the 
slopes. 
The depth of this valley was at least 500 to 600 feet. Between the 
dikes and the tufa, then, we find the limiting evidence which enables us to 
say very confidently that two-thirds to three-fourths of the present depth 
of the inner gorge has been excavated since the activity of that crater. As 
to the age of the crater itself, all that can be said is that it looks very recent. 
Except for the undermining of a considerable part of it by the recession of 
the great wall beneath, its preservation would be quite perfect. Still a 
nearer view might reveal evidences of antiquity which could not be dis- 
cerned when viewed across the chasm from Vulcan’s Throne, at a distance 
of nearly two miles. But, in any event, there is one conclusion most deeply 
impressed upon the mind : that this great inner gorge, vast as it is, has been 
excavated in a period of time which, judged by the geological standard, has 
been very short. The work has been done with a rapidity much greater 
than might otherwise have been supposed. The processes which have been 
so exceptionally active here are two — 1st, corrasion, and 2d, the undermin- 
ing of the wall of the inner gorge. 
West of Vulcan’s Throne there is a place where it is practicable to de- 
scend from the esplanade to the river. The way is difficult and at times 
well calculated to daunt the most active climber The wall is here much 
broken down and the vertical face has given place to a very steep slope. 
The descent is upon the cascade of lava which has flowed down the Toro- 
weap and poured into the abyss. Upon any ordinary rock the descent 
would be impracticable ; but the roughness of the basalt gives admirable 
foothold, and there is no difficulty of a serious nature in passing the steep- 
est places. The worst part is near the bottom, where the scouring of the 
river has left a nearly vertical wall 400 feet high. But there are several 
crannies where a precarious foothold may be obtained, and the river may 
be reached with less difficulty than might have been anticipated. Very 
seldom is it possible to descend in safety the walls of the Grand Canon. 
At the brink of the river there is little to call for special mention here. 
To the imagination must be left the task of picturing the aspect of the walls 
7 G c 
