64 GENERAL COXCLrSIOXS. 



spread. Falliug on the land it will be washed away by 

 erosion or enter as an inconspicuous component in the 

 coarser atmospheric dust, and falling in the sea it will be 

 lost among the more copious aqueous sediments there. 

 unless places exist where these are absent. On account 

 of this slow settling of the finest dust we cannot expect 

 to find it forming- separate laminae in eolian deposits. 

 for over regions where these are built up. the wind will 

 never remain quint long enough to permit a sufficient 

 quantity of only finn material to settle and form such 

 layers. *j It a])pears therefore that the finest wind sedi- 

 ments, whicli may be laid down in such quantity as to 

 form appreciable deposits, consist in the main of j^articles 

 ranging fi'om coarse to fine dust, and do not have any 

 markedly laminated structui*e. 



SUMMAKT. 



The work of the atmosphere begins with erosion. This 

 erosion is confined to murh smaller areas than atmos- 

 pheric sedimentation. One such area of erosion maybe 

 regarded as one of the corners of an isosceles triangle, 

 pointing agaimst the wind. Between the two equal sides 

 of this triangle ti'ansportation and sedimentation is tak- 

 ing jilace. The Cjuantity of work pei-formed is greatest 

 near the area of erosion. In this area materials of varied 

 coarseness are moved, up to pebbles which measure at 

 least eight millimeters in diameter. Deposition of the 

 coarsest material, such as gTavels. takes place imme- 

 diately. They are left as a thin veneer on the surface, 



*) It is interesting to notice that separate layers of snch fine material are 

 seldom absent from the silts and clars deposited in water. 



