bRIFTING SAND. 



13 



composition. Thii-ty-eight samples have been analyzed, 

 coming from eleven different localities. These it will be 

 well to briefly describe, together with the sand from each 

 place. 



On the north side of the Mississippi river at New Bos- 

 ton in Illinois an ancient terrace is blown up into a sand 

 ridge about a mile in length. From all appearances the 



Table III. Mechanical Composition of Dune Sand from New Boston, Ills. 





31 



33 



33 



24 





Leogth of 



diameter in 



mm. 



Rear slope of 



ripples In dune 



sand. 



Dane sand. 



Top of ripple In 

 dune sand. 



Front slope of 

 dune. 



Average. 



16-8 













8—4 



.6 









•^ 1 



4-2 



2.8 











.7 



2-1 



2.0 





.1 







.5 ' 



1-^ 



9.9 1 



2.6 1 



29.6 ■ 



3.6 





11.4 1 



i-i 



30.4 h 



31.8 h 



56.0 fa 



30.8 



■ 



37.2 ■ 



i-i 



47.8 ■ 



64.4 h 



13.6 1 



63.6 



■ 



47.3 ■ 



¥ 16 



5.0 \ 



.6 ' 



.2 ^ 



2.0 





1.9 



l¥ 32- 



.4' 







1.0 





.3 



i^-i^ 













sV-rb 













ISS iSli 

















sand in these dunes has not yet travelled a half mile. The 

 materials in the original terrace are quite heterogenous in 

 composition (Tab. I). The coarse grades have not yet 

 had time to be quite left behind but appear in a small 

 quantit}' in some of the dune sand (no. 21). One of the 

 samples (no. 23) was taken by skimming the surface on 

 the crest of a ripple. This is unique among all the anal- 

 yses of typical dune sand in having medium sand as its 



