MIRAGE—CLEARNESS OF THE AIR—FOSSILS. 108 
northerly, or from the mountains towards the low valley of the desert. Several of the beds 
were strongly colored by peroxide of iron; and gypsum, in clear plates, (selenite,) abounded in 
one of the lowest. No fossils could be found, but the strata were evidently comparatively 
recent, and are probably Tertiary. 
As night came on, a mirage was seen in the direction of the Colorado river; the distant moun- 
tains loomed up with curious outlines. We were almost exhausted from exertion and want of 
water. The poor mules began to fail, and cried out in their peculiar, plaintive manner, evi- 
dently desiring water. As we neared the foot of the slope of the sedimentary strata, we found 
sand drifted into hills and banks like snow-drifts. These extended for a long distance on our 
left, and we travelled around and among them until we were suddenly stopped at the brink of 
a deep ravine, with precipitous banks of clay like those we had passed the previous night. Nu- 
merous specimens of Anodonta were found on the surface. It being nearly dark, it was decided 
to rest the animals until the moon arose before we attempted to cut a roadway down the sides of 
the chasm. At half past ten in the evening we succeeded, after great difficulty, in getting the 
train over, and then directed our course for another projecting range of hills, dimly visible by 
moonlight in the distance. The route was smooth, with the exception of an occasional drift ot 
sand, for about three miles, and then we found a second great ravine, which caused considerable 
delay. 
The extreme purity and clearness of the atmosphere on this desert becomes strikingly evident 
at night. The sky remained unclouded ; and the stars shone out with that number and bril- 
liance so characteristic of clear, frosty nights in the north ; and the moon rose above the horizon 
with a clear, round disc, apparently unmodified by any vapors near the ground. 
We travelled steadily along, all night, but found no signs of the emigrant road. Every hour 
became precious, for the mules were nearly exhausted ; many had given out; and it became 
evident that the wagons and all heavy articles must soon be abandoned, in order to press for- 
ward for water. About four o'clock in the morning a change in the atmosphere was perceived ; 
there was an occasional dampness, or sudden coolness, together with the odor of vegetable 
decomposition. These whiffs of cool, damp air were mingled with the dry, warm breezes of the 
Desert, and could be readily distinguished from them. The mules of the train were the first to 
recognize these indications of the proximity of water, and they became animated and pressed 
forward with eagerness. The riding mules pricked their ears and snuffed the air, while those 
that had been allowed to run loose in the rear of the wagons charged forward in a gallop. We 
soon reached. the brink of a chasm or ravine in the clay similar to those before described, except 
that there was a small shallow stream of water at the bottom. The cry of ““Water!”” arose from 
those who first reached it, and it was repeated with loud shouts of joy from one end of the train 
to the other. 
The stream was very shallow and the current sluggish, flowing over a bed of clay alone, 
Which was so soft thatit was hardly possible to cross it. In some places there was a border of 
green canes, tule, and coarse grass, which afforded a little refreshment to the animals. This 
water was strongly impregnated with common salt and sulphate of magnesia, and it deposited 
athick saline incrustation on the borders of the shallows along its course. It was not very dis- 
agreeable to the taste, but coffee made with it was exceedingly nauseating. Its temperature at 
sunrise on the 20th of November was 48°; the air 40°, and at 12 m. 90°. Shells of all the 
species before observed were found here in aburidance, and, in addition, several small and thick 
bivalves, (Gnathodon Lecontei. With the exception of the Gnathodon, these were abundant on 
the surface, but were not found in the clay of the banks. 
eg 
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