DUST AND SAND STORMS IN THE WEST. 663 



storms appear to be about twenty- five miles an hour. Velocities 

 two and a fyalf times as high as this are not unknown, and the 

 efficiency of such a current is two hundred and five times that of 

 one having a velocity of twenty- five miles an hour. If the ve- 

 locity is doubled it increases the transporting power sixty-four 

 times. Should such storms then occur on twenty days of the year 

 instead of on two, the total work would be six hundred and forty 

 times more effective than in the first instance. Still another in- 

 crease would result from the greater vertical dispersion of the 

 lower greater load in a wind with high velocity. A predomi- 

 nance of aerial transportation may, of course, also be due to local 

 inefficiency of the aqueous work. But this digression is not 

 made for the purpose of proving the possibility of such a pre- 

 dominance in any place. A proof of this would be superfluous, 

 since the topography of sand-hill regions is conclusive evidence 

 on this point. It is merely desired to emphasize the fact that 

 atmospheric work is subject to very great range in its effective- 

 ness, and that as a consequence the great range of the estimates 

 made above does not impeach their trustworthiness. 



Some other stray items of information, culled from the news- 

 paper accounts, may be briefly stated in closing. The only state- 

 ment from which the distance over which dust has been trans- 

 ported can be definitely estimated is in a notice coming from the 

 southern part of California. From the notice made it is certain 

 that dust must have been carried twenty miles. Of course, this 

 does not speak against the possibility of a transportation over 

 twenty times that distance. In one case a slow settling of fine 

 dust from the air is reported as actually observed, and this was 

 also in California. The maximum wind velocities reported in 

 connection with dust storms are few, running from 36 to 90 miles 

 per hour, viz. : 36, 40, 45, 50-60, 90. Some instances of the erosive 

 effects of blown sand are described. It is stated that winds will 

 raise dust on sparsely covered, not cultivated land ; that orange 

 trees in California are sometimes girdled near the ground by sand 

 blasts ; that the glass in the windows of railroad coaches is etched 

 by impinging sand ; and that paint on the coaches is worn off in 

 the same way. The softer wood in telegraph poles is sometimes 

 worn away by sand so much faster than the harder wood in the 

 knots that the latter are left protruding far out. Finally, there 

 are some accounts of the coarseness of the transported material. 

 It is generally fine enough to be called dust, but sand is often 

 mingled with the dust, and occasionally there is fine gravel. Two 

 reports mention pebbles, and in one instance these are said to 

 have been large enough to " knock a man senseless." 



To the writer the facts here presented appear most interesting 

 in their incompleteness. While there are tens of thousands of 



