160 
THE GEAND CASOE DISTEIGT. 
Here a rain gully has cut a steep trough in the sandstone which, by 
its very roughness, permits us to descend, or rather slide down, at moderate 
risk. With one man to pull on the halter and two to push, each animal 
may be launched on its adventurous journey. The sandstone is scoured 
into a series of maximum and minimum slopes, all of them bare rock, and 
by sliding helplessly down the former and checking themselves upon the 
latter, the poor beasts escape perdition. The thickness of the sandstone thus 
traversed is about -!350 feet. At its base we find the lower Aubrey, which 
presents a less difficult aspect. It now remains to find the passage of the 
Red Wall, which is ten miles distant, and in the mean time we must descend 
a thousand feet of sandstones which make up the lower Aubrey. These 
consist of innumerable beds, varying in thickness from five feet to fifty, 
each presenting its own ledge and talus. The ledges are often beveled and 
notched by rain gullies, and wherever the way seems easiest we alternately 
travel along the talus and slide or scramble down the broken ledge to the 
next talus below. For several hours the journey consists of this kind of 
travel. Here the trail heads some offshoot of a great lateral gorge, there 
it rounds some lofty promontory. Often the shelf on which we move nar- 
rows to a mere fillet with imminent rocks above and destruction below. 
Had not the trail been already chosen we should find the shelves gradually 
vanishing, the ledge below becoming a single face with the ledge above. 
As it is the trail needed in many places to be built up to give a narrow 
tread along some projecting shoulder, where the packs brush the rocks as 
the mules pass by. At length it becomes steeper, the ledges more frequent 
and higher, and the way grows somewhat alarming. A single inadvei’t- 
ence, the slightest accident, sends man or beast to the great unknown. 
At length we reach the summit of the Red Wall limestone and a vertical 
cliff 1,200 feet high is below us. Here the trail doubles on itself and turns 
back at a lower level, following the brink of the cliff for three miles. At 
the end of this stretch is the summit of a steep but practicable slope across 
the Red Wall. Again the trail doubles in its course and a rapid descent 
of 2,000 feet brings us with no further danger to Surprise Valley. 
We seem to be in a ciil de sac. On the right is the great Red Wall preci- 
