SMOOTH SURFACES OF THE DRY LAKES OR PLAYAS—RIVERS. 221 
ever, probable that the peculiar illusive appearances of lakes of water, and the distortion of the 
images of rocks and trees, so common on plains and deserts, is the result of both reflection and 
refraction. 
The dry lake-bed was connected by a narrow strait, also dry; with a much broader and longer 
lake-bed extending far to the north, among the Lost Mountains. Other similar dry lakes were 
found among the ridges east of the Mojave River and at the lower end of this stream, which 
appears to terminate in a depression of this kind. 
On the hard, dry clay of one of these lake-beds I noticed very peculiar markings, like the 
tracks of an animal, extending for long distances in straight lines. These marks consisted of 
little depressions recurring at regular intervals; some of them appeared as if formed by the 
drawing or trailing of some irregular but light body over the surface when it was moist and 
yielding. The similarity between some of these marks and the trails of animals was very 
striking, and it was some time before their origin could be ascertained. "They had been pro- 
duced by branches of shrubs, with projecting limbs, that had been driven before the wind, the 
projecting limbs or knots having made prints at regular intervals by the rapid rotation of the 
branch. If such trails were covered up by a fresh deposition of clay, and should be afterwards 
exposed to view by splitting the layers, they would possibly be regarded as the tracks of a non- 
descript animal. 
These broad and smooth lake-beds, unobstructed by vegetation, offer a free scope for the wind, 
. Which sweeps over and keeps them perfectly clean, not a particle of sand or loose dust being 
allowed to rest on the mirror-like surface. The phenomenon of high, slender, whirlwinds of dust 
was often observed when we were in the vicinity of these dry plains. They rise high in the air, 
and are very distinct in their outlines; they progress from one side of a lake-bed to the other, or 
travel over the more uneven slopes, and do not remain in a perfectly vertical column, but are 
curved and bent in various directions, conforming to the currents of the air. 
A portion of the clay forming the surface of one of these dry lakes was preserved and exam- 
ined by the microscope, without finding any organic remains. It appears to consist principally 
of clay and fine sand, and is a stratum that is retentive of moisture. This fact is important in 
connexion with the discussion of the probability of obtaining water in the Basin by boring. 
According to the descriptions of Lieutenant Parke and others, the dry lakes, or Playas, of the 
region south of the Gila, in Sonora, are very similar to those of the Basin, and doubtless have a 
similar origin. The region in which they are found is in many respects very much like the 
Southern end of the Great Basin. s x 
STREAMS AND SPRINGS OF THE SOUTHERN PART OF THE GREAT BASIN. 
The dessicating influence which is exerted upon the ocean winds, in their passage towards the 
interior, by the lofty summits of the Sierra Nevada is so great as to prevent the precipitation of 
much moisture upon the barren ridges of the central parts of the Basin, or upon those ridges 
Which are near the eastern foot of the snowy ranges. 
A portion of the water which is thus intercepted in its passage to the interior, and deposited 
on the Sierra Nevada, flows down in sireams on the interior slopes, and reaches the borders of 
the Basin. The quantity thus discharged into the interioris by no means small, but is not 
Commensurate with that which flows down on the seaward slope of the chain. On the Basin 
side, the streams are few, at great intervals, and are generally short, and of small volume; on 
the other, they are numerous, ramified, and by constat confluence produce long and formidable 
