ATMOSIMllOliir DUST. 



33 



ferent conditions of deposition, and troni diftVrent local- 

 ities. 



Before discussing" the composition of these samples it 

 may, however, be well to note the nature of some wind- 

 borne sediments which have been carried by the atmos- 

 phere under more than ordinai'ily favorable circum- 

 stances, and in currents of more than ordinary strength. 



Such is the sand and dust stirred up from the roadbeds 

 by running railroad trains. Quartz particles considerably 

 larger than fine sand are here moved nearest the ground. 

 But the material which is lifted high enough (five or six 

 feet) to come in through the windows and doors of pas- 

 senger coaches is much finer. 



Among thirteen samples of such material collected in 

 coaches in different parts of the United States only one 



Table XX. (Continued). 



8.5 



86 



87 



88 





Frnm Western 

 MiDnesnta. 



From Eastern 

 Colorado. 



From Kansas. 



From Idabo and 

 Washington. 



Average. 



1:0 I 



49.0 ■ 



43.1 ■ 

 4.9 



.5 



1.0 

 22. S 1 

 65-2 Emm 

 10.2 ^ 

 .5 ' 



.1 . 



36.8 b 



57.0 Hi 



4.6 



.5 r 



.3 



54.8 ^ 

 41.6 W 

 3.3 

 .1 



tr. . 



6.4 \ 

 36.6 ■ 

 42.9 ■ 

 10.3 1 



2.9 

 2 



