390 



CHESTER K. WENTWORTH 



The scheme of class terms presented below was devised by the 

 writer after a somewhat extensive consideration of several more 

 complicated classifications. These were characterized by more 

 extensive use of the adjectives coarse and fine and by the use of 

 many combinations and permutations of several grade terms. 



These were all rejected in favor of the simpler plan here 

 presented because of the seeming futility of attempting to make 

 detailed quantitative discriminations by use of a verbal scheme. 

 Such discrimination can be satisfactorily made only by graphic 

 or tabular methods and the writer believes the simpler classification 

 will be most generally acceptable and therefore most useful in the 

 study of sediments. 



The table shows only class terms for aggregates; the proper 

 rock terms will be chosen and used in an analogous manner. 



Certain materials of sedimentary origin but highly variable 

 composition, notably glacial till, will not fall into any of the divi- 

 sions of the table above. No attempt has been made to make an 

 all-inclusive scheme. Till is known by its extreme range of 

 mechanical composition and by definition, therefore, will not fit 

 into so simple a classification. The test of any classification is in 

 its applicabihty to natural objects. The terms here proposed 

 were tested by reference to a large number of analyses made by 

 Udden.' By inspection of about fifty of these chosen at random 

 it was found that only the analyses of till did not accord with the 

 specification given for one of the terms, and that each of the other 



' J. A. Udden, loc. cit. 



