EOLIAN TRANSPORTATION 59 



over which quartz particles of different dimensions may be lifted by 

 moderately strong winds in single leaps. (Udden-99: dj.) 



Gravel (diameter from 8-1 mm.) * A few feet. 



Coarse and medium sand (diameter 1-14 mm. 1-0.25) Several rods. 



Fine sand (diameter y^-Ys mm. 0.25 — 0.125) Less than a mile. 



Very fine sand (diameter y^-yiG mm. 0.125-0.0625) A few miles. 



Coarse dust (diameter i/^g -ys2 mm. 0.0625-0.03125) 200 miles. 



Medium dust (diameter i/^o-i^j^ mm. 0.03125-0.015625). . . 1,000 miles. 



Fine dust (diameter 1/^4 mm. 0.015625 and less) Around the globe. 



These theoretical distances are probably never realized, owing to 

 the complex character of the wind currents and other factors. 



Dust storms may often cover extensive areas and be the means of 

 distant transportation of materials. Udden (gS: ip6) records 

 storms extending 300 and 400 miles in their longest observed direc- 

 tion. A Chinese dust storm is known to have existed simultane- 

 ously from Hankow to Chin-kiang, or over a distance of more than 

 450 miles, and for an unknown distance beyond in either direction. 

 (Guppy-38.) On February 6 and 7, 1895, dust fell in Mis- 

 souri which must have come from western Kansas and Nebraska, 

 since all the intervening country was covered with snow and ice. 

 On April 2, 1892, a yellow dust carried from the interior of China 

 fell on the deck of a ship 95 miles west by south of Nagasaki, at 

 least 1,000 miles from its source; and dust storms from Australia 

 have sometimes reached New Zealand, having been transported 

 some 1,500 miles. Dust believed to have been brought from the 

 Sahara has been observed in northern Germany, and in England, 

 some 2,000 miles distant. This is the so-called sirocco or trade- 

 wind dust, which, however, has little or no relation to the true si- 

 rocco. Volcanic dust carried to the upper air is likewise trans- 

 ported over great distances. Thus the dust formed by the eruption 

 of Krakatoa in 1883 was projected so high into the air that, caught 

 by the currents of the upper air, it was carried around the world 

 repeatedly before settling. Some of this dust is said to have com- 

 pleted the circuit of the earth in 15 days. (Chamberlin and Salis- 

 bury-i6:^7.) This dust settled slowly all over the world and 

 became incorporated in all contemporaneous deposits. Beds of vol- 

 canic dust in places 30 feet thick are known in Kansas and Ne- 

 braska, hundreds of miles distant from volcanoes which could have 

 supplied the material. (Salisbury-82.) The following summary of 

 volcanic dust transport is taken from Free (33:1^9-/50) : "Vol- 

 canic dust from Iceland has several times fallen in Scandinavia, in 



* See table of sizes of sand grains, etc., in Chapter VI, page 287, 



