FUNDAMENTAL CAUSE OF SORTING 931 



diagrammatic forms, has failed to bring to light many new and significant 

 features of individual analyses worthy of mention. It, however, does not 

 prove that such features are not present and will not be gradually broughr 

 to light. 



"Monograms" of various Kinds of Deposits 



However, groups of analyses, each belonging to a single class of de- 

 posits, when taken together, show much greater promise of diagnostic 

 features. If 10 analyses of dune sand taken at random be plotted in the 

 form of cumulative logarithmic diagrams, and these diagrams be super- 

 posed, a figure is obtained which at present seems to be characteristic of 

 dune sand. Other groups of 10 dune sands taken at random are found 

 to give figures of closely similar form. The writer has fallen into the 

 habit of calling these figures "monograms," for each consists of lines 

 crossing each other in various ways, and the form of the network, as well 

 as of the individual lines, seems to have significance. 



The similar plotting of groups of 10 analyses of other kinds of sedi- 

 ments lends strong support to the notion that monograms prepared in 

 this way may in some cases be diagnostic of the kind of sediment. If 

 10, 20, or 50 analyses of the Dakota sandstone were made, it seems very 

 doubtful if, in the present state of knowledge, any single analysis would 

 of itself throw much light on the conditions of the deposition of the sand- 

 stone; but if all were plotted one on another, the resultant compound 

 figure might throw a great deal of light on the genesis of the deposit. 



The writer would like to emphasize an inference already made by other 

 investigators, but not yet generally appreciated, this inference being that 

 most limestones were once clastic, and the particles were sorjted before 

 final deposition. Thus limestones which are not too extensively recrys- 

 tallized can be studied as though they were sandstone or conglomerate. 



Conclusion 



Although, as is shown by both theory and observation, many factors 

 affect the sorting of each kind of sediment, the principal underlying cause 

 of sorting is the difference in the friction involved in the movement of 

 particles of different sizes through a fluid. With occasional exceptions, it 

 is not yet possible to infer correctly the origin of a sediment from a me- 

 chanical analysis, yet it seems probable that by further study more and 

 more significance will be found in such analyses; in other words, that a 



