GEOLOGY. 287 



hardness of the gem, also stood out in relief forming an elevated string, osar- 

 like, under their Ice. When the surface acted on was vertical and charged 

 with garnets, a very peculiar result was produced; the garnets were left 

 standing in relief, mounted on the end of a long pedicle of feldspar, which had 

 been protected from action while the surrounding parts were cut away. These 

 little needles of feldspar tipped with garnets, stood out from the body of the 

 rock in horizontal lines pointing, like jeweled fingers, in the direction of the 

 prevailing wind. They form in reality a perfect index of the wind's direction, 

 recording it with as much accuracy as the oak-trees do hi the region about 

 San Francisco, where they are all bent from the perpendicular in one direction, 

 or hi some places lie trailing along the ground. AIL these little fingers of 

 stone pointed westward, in the direction of the valley of the pass, to which 

 the wind conforms. "We experienced the wind before reaching the point of 

 rocks and the sand drifts : it blew with great violence and seemed to be a 

 great air-current, as uniform in its direction and action as the great currents 

 of the sea. It flows into the interior with singular persistence and velocity, 

 sweeping down over the slope of the pass, not in fitful gusts and eddying 

 whirls, but with a constant uniformity of motion unlike any of the winds of 

 our Atlantic seabord, or of the plains. The pass would, in fact, seem to be a 

 great draught-channel or chimney, to the interior, through which the air 

 makes 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 heated desert. This pass 

 is the only break of any magnitude in the mountain 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 Sacramento 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 on. On the upper plain, north of the sand hills, where steady and 

 high winds prevail, and the surface is paved with pebbles of various colors, 

 the latter are all polished to such a degeee 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 lacquered ware, or as if the pebbles had been 

 oiled and varnished. On the lower parts of the desert, or wherever there is a 

 specimen of silicified wood, the sand has registered its action. It seems to 

 have been ceaseless 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 contact 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 trans- 

 ported by currents in a fluid. If we can have distinct abrasion and linear 

 grooving of the hardest rocks and minerals by the mere action of little grains 

 of sand falling in constant succession and bounding along their surface, what 

 may we not expect from the action of pebbles and boulders of great size and 

 weight, transported by a constant current in the more dense fluid, water ? 

 "We may conclude that long rectilinear furrows of indefinite depth may be 



