I. Ad iii;A\i:i.s. 



sand dunes: 2] drifting' wand, con.stitutiiiu- tln' familiar 

 dunes in dry and sandy regions; 8) fine sand, wliicli is 

 soon dropped hy tlie wind in llielec of di-ifting dnnes : 4) 

 and (Inst, which only slowly settles out of the air far 

 away from the place where it was raised. 



Numerous observations on known eolian deposits in 

 the field and on the mode of action of the wind have also 

 been made to supplement this special study of the mechan- 

 ical composition of wind sediments, and these will be 

 drawn uiion in the discussion of the other data. 



LAG GRAVELS. 



In many places where atmospheric erosion is going on. 

 streaks of gravel are to be seen, partly covering the 

 ground. Most often this gravel forms a thin veneer 

 which partly protects the ground from fui-ther erosion. 

 Though the present position of this material is due to the 

 action of the wind, it is quite evident that it has not been 

 transported very far. The deposits from which it has 

 been derived may lie close by, and they are never far off. 

 Commonly it is a bank of sand, part of which has been 

 removed. The finer grades have been blown away, expo- 

 sing these larger fragments to the force of the wind, which 

 apparently moves them by undermining and i-olliug. 

 They sometimes occu]»y the hollows on the eroded 

 ground. It is evident that the coarseness of this gravel 

 renders it much less subject to the action of the winds 

 than the finer materials. Occasionally it may be found 

 partly or wholly covered by finer materials, but on the 



