GKXEIiAL CO.NCLI SIOXS. i'yli 



else by the subsequent supevflcial mixing- effected by 

 various forces. Such mixing- results from the direct 

 action of the winds ; indirectly, from the action of the 

 wind on various objects which are caused to move on the 

 surface of the ground; from rain; from trost; from the 

 works of insects and other small animals; and fi-om 

 growing- plants. All these agencies acting- together can 

 hardly fail to prevent any sub-aerial deposit of dust from 

 acquiring- such a fine lamination as is often seen in silts 

 and clays, which are deposited under water and which 

 have accumulated much more rapidl}'. Eolian loess is 

 never markedly laminated, and the primary cause of the 

 absence of this structure is the great velocity' of the 

 atmospheric currents, which scatter the materials in sus- 

 pension over so wide areas that the deposit from each 

 passing current becomes too small to remain as a dis- 

 tinct laver. 



These analyses plainly indicate that atmospheric sedi- 

 ments are rendered uniform also by the elimination of the 

 finest particles, such as measure less than one one-hundred- 

 and-twenty-eigth of a millimeter in diameter, and eA'en to 

 some extent the particles of the next coarser grade. It 

 will be noticed that the ver^- fine dust in but a few cases 

 exceeds three per cent of the total weight of each sample 

 examined. The fact that this fine material is not spe- 

 cially abundant in the dust caught on the calmest days 

 indicates that it is easily held in suspension. This is no 

 doubt the kind of dust which follows the wind around the 

 globe. It is carried everywhere and must be settling 

 everywhere in exceedingly small quantities, inversely pro- 

 portionate to the greater area over which it is being 



