side, and if greater than unity, the maximum sorting lies on the fine side. If Sk 

 is equal to unity, the curve is symmetrical, and sorting is uniform on both sides 

 of the frequency curve. Figure 6-3 shows the cumulative-frequency curves and 

 the statistical parameters obtained from the curves of three different types of 

 sands. 



Interpretation of Data 



Probably in no geologic procedure have statistical methods been used more 

 than in the interpretation of size analyses. A review of recent literature indi- 

 cates that modern sedimentary petrologists must have a working knowledge of 

 statistical methods. There is, however, some difference of opinion as to the 

 value of these statistical methods. Krumbein and Pettijohn (1938) state: 



The preceding sections on correlation, the X 2 test, the theory of control 

 and the probable error indicate that there is a growing recognition of 

 the importance of statistical analysis in sedimentary problems. One 

 cannot ignore the contributions which such studies have made and will 

 make to a fuller understanding of the complex study of sediments . . . 



On the other hand, Twenhofel and Tyler (1941) comment: 



Statistical methods of study may ultimately be shown to have more 

 value than is now apparent. Statistical results certainly permit rapid and 

 easy comparison of large numbers of sediments and render it simple 

 to point out similarities and differences. What significances the results 

 have in terms of environmental conditions remain to be determined. 

 So far as the writers' survey of the field is concerned, the best that 

 may be stated is that the significances of the studies are not apparent. 

 Statistical studies certainly permit extensive use of mathematical for- 

 mulae which are of interest to those who are mathematically inclined. 

 The writers have found these formulae of great interest, but not par- 

 ticularly useful so far as interpretation of the sediments are concerned. 



Pettijohn (1949), in commenting on the various objectives of mechanical 

 analyses says, "Greatest effort and greatest disappointment have centered about 

 the last of these objectives (identification of agent or environment). The results 

 to date have not been up to expectations." 



Emery (1954), in discussing average median diameter, sorting coefficient, 

 percent of CaC0 3 and percent of organic matter of sediments from various 

 recent environments in Southern California, states: 



It must be emphasized that table I cannot be used as a reliable basis 

 for determining the probable environment of deposition for a given 

 sample. The table merely lists the average values of several parameters 

 for different environments of southern California. In each environment 

 there is considerable variation. Under different climate or source con- 



102 



