306 Tertiary. 



lee. When the surface acted on, was vertical and charged with gar- 

 nets, a very peculiar result was produced; the garnets were left stand- 

 ing 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. 



The effects of driven 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 surface is paved 

 with pebbles of various colors, the latter are all polished to such a de- 

 gree that they glisten in the sun's raj's, 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 specimen 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 contact have worn away all 

 their little asperities and become almost perfect spheres. This form is 

 evident whenever 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 in a fluid. 

 If we can have a 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 on their surface, what may 

 we not expect from the action of pebbles and bowlders 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 made by loose materials, and that it is not essential to 

 their formation that the rocks and gravel, acting as chisels or gravers, 

 should be pressed down by violence, or imbedded in ice, or moved 

 forward en masse under pressure by the action of glaciers or stranded 

 icebergs. Wherever, therefore, we find on the surface of moun- 

 tains, not covered by glaciers, grooved and polished surfaces with 

 the furrows extending in long parallel lines seeming to indicate the ac- 

 tion of a former glacier, we should remember the effects which may be 

 produced during a long period of time by light and loose materials 

 transported in a current of air; and which, consequently, may be pro- 



