DlSCtJSSlOK OI' DATA 741 



From this table we see that in water deposits the chances of finding 

 boulders or pebbles having a diameter 4,096 times as large as the diam- 

 eter of the smallest grain of sand or clay in the same deposit are about 

 equal to finding in a wind deposit pebbles or sand grains which have a 

 diameter 256 times the diameter of the finest dust grain in the same de- 

 posit. We also note that the chief ingredient in water deposits contains 

 about 5 per cent less than it usually does in wind deposits. The admix- 

 tures of the first order contain about 2 per cent less in water sediments 

 than in wind sediments. In all the other admixtures the percentages 

 are higher in water deposits, grade for grade, than in wind sediments. 



Difference in the coarseness of the chief ingredient. — If we examine 

 the coarseness of clastic elements present in the maxima of different 

 samples, we find that the range in wind deposits is through eight grades 

 and of water deposits is through 13. In tabular arrangement we find 

 the distribution of maxima as below. In their chief ingredient some 

 water deposits are coarser and some finer than any wind deposit. 



Table showing the Number of Maxima in different Grades in all Sediments 

 \ examined 



Diameter in millimeters. Wind sediments. Water sediments. 

 32-16 \ ] |... .. 3 



, ; ,16-^.. H....^-s.. .>^>.;.., .>M. ./;..;..„.' [..: . .... 6_ 



I 8-4.! I I • :.... |.. . 17 



I ^-2.-......l...^..l..v.. ...... ,...-..../. *;■.' 4 ■■ 



2-1....... ^4 5 



1-1/2 4 24 



1/2-1/4. 11 10 



1/4-1/8. 55 51 



1/8-1/16 10" 18 



1/16-1/32 27 30 



1/32-1/64. 42 15 



1/64-1/128 1 11 



1/128-1/256 1 



» The small number of samples of wind sediments that have grains from one-eighth 

 to one-sixteenth millimeter in diameter in their maxima shows that more collections 

 would he desirable. Six of the ten samples of this material were collected from railroad 

 coaches and from houses ; one is volcanic dust, one was taken near a wagon road, and 

 one came from a plowed field. Deposits of the fineness of these samples do not drift as 

 dunes, but in dry and semi-desert regions they drift extensively and form flat stretches 

 of land in the lee of dune regions and over many high plains. I have made other obser- 

 vations which convince me that if dust were collected on the western plains and plateaus 

 in the same manner as I collected it in Illinois, the gap in the above table would be 

 filled. 



