656 J. A. UDDEN COMPOSITION OF CLASTIC SEDIMENTS 



Page 



Incipiently blown sand 682 



Lee sand .' 682 



Dust 683 



General discussion 683 



Miscellaneous collections of dust 683 



Dust collected by apparatus from the atmosphere 686 



Dust taken on surfaces above the ground 688 



Shower dust 689 



Tables of mechanical analyses 692 



Till (Table 1) 692 



Water deposits (Tables 2 to 20) 693 



Wind deposits (Tables 21 to 29) 713 



Sands containing magnetite (Table 30) 727 



Loess (Table 31) 728 



"Gumbo" (Table 32) 729 



General discussion of data 730 



Modes of sedimentary sorting 730 



Law of the chief ingredient 732 



Law of decreasing admixtures 733 



Law of the sorting index 735 



Law of the secondary maximum 736 



Differences in sediments due to different modes of work 738 



Washed sediments 738 



Drift and blown material, silt, and dust 738 



Differences between water and wind sediments 740 



General discussion 740 



Difference in grade distribution 740 



Difference in coarseness of the chief ingredient 741 



Difference in the quantity of the chief ingredient 742 



Difference as to average number of grades 742 



Difference in uniformity of composition 743 



Restrictions in the application of some characteristics 743 



Introductory 



In an earlier paper- I have published mechanical analyses of a num- 

 ber of samples of wind sediments and have described the conditions 

 under which these samples were formed, classifying them into lag 

 gravels, drifting sand, lee sand, and atmospheric dust. It was my pur- 

 pose to present some reliable measurements on the mechanical composi- 

 tion of such deposits. It was evident from that study that wind sedi- 

 ments are less heterogeneous in their mechanical make-up than water 

 sediments are. This fact is quite generally recognized. It is readily 



2 The Mecliauical Composition of Wind Deposits. Angustana Library Publications, 

 Number 1. Rock Island, Illinois, 1898. 



