7l6 STUDIES FOR STUDENTS 



self while geologist of the Wheeler Expedition west of the looth 

 meridian in 1878. In acting on the hard rocks the sand cuts so 

 slowly as at times to produce only grooved or fantastically 

 carved surfaces often with a very high polish. The geologists of 

 the 40th Parallel Survey in 1878 described like interesting phe- 

 nomena as observed on the western faces of conglomerate bowl- 

 ders exposed to the sand blasts of the desert regions of Nevada. 

 The surface of the otherwise light colored rock was found to 

 have assumed a dark lead gray hue and a polish equal to that of 

 glass, while the sand had drilled irregular holes and grooves, 

 often three-fourths of an inch deep and not more than an eighth 

 of an inch in diameter, through pebbles and matrix alike. 



Even the humid east is not without its illustrations of natural 

 sand-blast carvings. On the shores of Cape Elizabeth, Maine, 

 the cliffs facing toward the open sea are often riddled with 

 peculiarly irregular holes formed by the gyrations of sand grains 

 blown up from the beach below and kept spasmodically in motion 

 by the wind. 



{B) CHEMICAL ACTION OF WATER. 



Pure water, although an almost universal solvent, nevertheless 

 acts with such slowness upon the ordinary materials of the 

 earth's crust that its results are scarcely appreciable to the 

 ordinary observer. It by no means follows, however, that its 

 effects are not worthy of our consideration here. This is par- 

 ticularly true when we reflect that the results we are discussing 

 are not merely those of days and weeks, but of years even when 

 counted by the tens of thousands and millions. Moreover 

 absolutely pure water, as a constituent of our earth and its 

 atmosphere, presumably does not exist. We have to consider 

 its action as well when contaminated with sundry salts and 

 acids which it almost universally holds, having taken them up 

 in passing through the atmosphere and in filtering through the 

 overlying layer of organic matter and decomposition products 

 which cover so large a portion of the surface of the land. It is 

 when thus contaminated, then, that are manifested the wonder- 



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