180 W. P. Blake on the Grooving and Polishing of Rocks. 
the sand drifts: it blew with great force and seemed to be a great 
air current, as uniform in its direction and action, as the great cur- . 
rents of the sea. It flows into the interior with singular persist- 
ence and velocity, sweeping down over the slope of the Pass, 
not in fitful gusts and eddying whirls, but with a constant uni- 
formity of motion unlike any of the winds of our Atlantic sea- 
board, or of the plains. 
The Pass would in fact appear to be a great draught-channel, 
or chimney, to the interior, through which the air rushes inland 
from the cool sea, to supply the vacuum caused by the ascent of 
a column of heated air from the parched surface of the great Des- 
ert. This Pass is the only break of any magnitude in the moun- 
tain chain for a long distance, and as an air-channel, holds the 
same relation to the Colorado Desert as is sustained by the Golden 
Gate, at San Francisco, to the broad interior valleys of the Sac- 
ramento and San Joaquin. , 
The effects of driving sand are not confined to the Pass; they 
may be seen on all parts of the Desert where there are any hard 
rocks or minerals to be acted upon. On the upper plain, north of 
the Sand Hills, where steady and high winds prevail, and the sut- 
face is paved with pebbles of various colors, the latter are all pol- 
ished to such a degree that they glisten in the sun’s rays, and 
seem to be formed by art. The polish is not like that produced 
by the lapidary, but looks more like laquered ware, or as if the 
pebbles had been oiled and varnished. 
On the lower parts of the Desert, or wherever there is a speci- 
men of silicified wood, the sand has registered its action. It 
seems to have been ceaselessly at work and when no obstacle was 
encountered on which wear and abrasion could be effected, the 
grains have acted on each other, and by constantly coming in con- 
tact have worn away all their little asperities and become almost 
perfect spheres. This form is evident when the sand is examined 
by a microscope. 
We may regard these results as most interesting examples of 
the denuding power of loose materials transported by currents 
ina fluid. If wecan have a distinct abrasion and linear grooving 
of the hardest rocks and minerals, by the mere action of little 
constant current in the more dense fluid-water? We may col- 
clude that long rectilinear furrows of indefinite depth may be 
made by loose materials, and that it is not essential to their forma- 
tion that the rocks and gravel, acting as chisels or gravers, should 
be pressed down by violence, or imbedded in ice, or moved for- 
ward en masse under pressure by the action of glaciers or stranded 
icebergs, Wherever, therefore, we find on the surfaces of moun- 
