FACTOKS AFFECTING SORTING 927 



or sand may or may not have its interstices filled or partly filled with 

 smaller grains. Apparently most mechanical analyses barely furnish 

 bases for guesses as to genesis, and often one guess is as good as another. 



Note on peevious Workers 



However, as Atterberg,- Mohr/ Thoulet/ Udden/ Gilbert/ Goldman/ 

 and others have pointed out, some analyses have significance, those of 

 dune sands in particular being commonly recognizable by the average size 

 of grain and high degree of sorting, tliough beach sand is also well sorted. 



Methods of making Analyses 



The principal methods which have been used in mechanical analysis 

 are the following: Hilgard, the eminent authority on soils, used both 

 screens and elutriating apparatus very extensively, and his separates 

 ranged in size from i^ mm. to 64 mm., the grains of each separate being 

 twice the size of those in the next finer separate. 



Atterberg's separates range from .001 mm. to 5 mm. His ratio was 

 not fixed, but is approximately 2. 



Mohr makes separates ranging from 10 mm. down to .0005 mm. by 

 allowing particles to settle through water, his finest particles requiring 

 a week to settle 20 centimeters. 



Thoulet uses a more irregular series of ratios ranging from 2 to 6, and 

 his separates range from .04 mm. to 15 mm. 



The U. S. Bureau of Soils makes separates ranging from .005 mm. to 

 2 mm. by the use of screens and centrifuges, and the ratio between sizes 

 ranges from 2 to 10. 



Methods of studying Analyses 



Diagrammatic representation is so advantageous as to be practically 

 requisite in the study of mechanical analyses. Two forms, which may be 



2 A. Atterberg : Die rationelle Klassifikation der Sand u. Kiese, Chem. Zeitung, xxix. 

 no. 15, 1905, pp. 195-198. Also his "tJber die Korngrosse der Diinensande," same journal 

 and volume, no. 80, p. 1074. 



^ E. C. .1. Mohr : Ergebnisse mechanischer Analysen tropischer Boden. Bull, de De- 

 part, de I'Agric. aux Indes neerlandaises, no. 47, Buitenzorg, 1911. 



* J. Thoulet : fitude bathylithologique des cotes du Golfe du Lion. Annales de I'lnst. 

 Oceanogr., Monaco, vol. iv, 1912, fasc. 6. 



^ J. A. Udden : Mechanical composition of clastic sediments. Bull. Geol. Soc. Am., vol. 

 25, no. 4, December, 1914, pp. 655-744. 



<* G. K. Gilbert : The transportation of debris by running water. U. S. Geol. Survey 

 Professional Paper 86, 1914. 



■^ M. I. Goldman : Petrographic evidence on the origin of the Catahoula sandstone of 

 Texas. Am. .Jour. Sci., 4th ser., vol. xxxix, March, 1915, pp. 261-287. 



