1. Improvement of classification and precision of nomenclature of 

 clastic sediments. 



2. Study influence of grain-size distribution on porosity and perme- 

 ability. 



3. Study of relations between dynamics of stream flow and trans- 

 portation of particulate materials. 



4. Quantitative studies of facies changes and correlations. 



5. Identification of agent or environment responsible for the origin 

 of the sediment. 



From the above it is apparent that size analyses are essential in the study 

 of clastic sediments. Complementing other data they frequently aid in the solu- 

 tion of many stratigraphic problems. 



Equipment- 

 Equipment normally required for size analyses is listed below: 



(a) A set of nested sieves, the scale of which may be either the Tyler or 

 the U. S. Standard. Table 6-1 gives the comparison of these two scales and 

 correlates them to the Wentworth size classification most commonly used by 

 sedimentationists. The combination of sieves used will depend upon the 

 sediment and the number of size groups desired. 



(b) A balance for weighing samples and sieve fractions. An ordinary beam 

 balance accurate to 0.01 gram is satisfactory. 



(c) An assortment of 250- to 600-milliliter beakers. 



(d) A rubber-tipped pestle or small wooden blocks for disaggregation of 

 samples. 



(e) A hand lens or binocular microscope for checking completeness of 

 disaggregation. 



If the sediment cannot be disaggregated because of the cementing material, 

 thin sections must then be prepared. The grains are counted and measured with 

 a petrographic microscope equipped with a mechanical stage and a micrometer 

 eyepiece. If the sediment contains an appreciable amount of clay and silt 

 particles, it may be necessary to subdivide this fraction. The equipment and 

 procedures used in the analysis of clay and silt particles are discussed by 

 Krumbein and Pettijohn (1938) and Twenhofel and Tyler (1941). 



Other equipment that will aid materially in size analyses is a rock crusher, 

 sample splitter, electric oven, and a Ro-Tap shaking machine. The ultra-sonic 

 cleaner used to clean tools and machine parts has been found to be very useful 

 in the disaggregation and cleaning of samples. (Gude, A. J., U. S. Geological 

 Survey, personal communication.) 



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