414 E. W. SHAW THE STUDY OF SEDIMENTARY DEPOSITS 



The physical investigations that have been considered seem to fall into 

 the following general classes : 



1. Field and laboratory studies of the action of present oceans, lakes, 

 streams, glaciers, wind, gravity, and frost, and the various products of 

 these agencies. 



2. The application of physical and geographic criteria to the study of 

 geologic strata and formations — 'their extent, thickness, stratification, 

 mechanical and mineralogic constitution, and color, and variations in 

 these physical characters. 



We need especially to know (1) more about the mechanical constitu- 

 tion of various kinds of strata and the extent to which their origin is 

 recorded therein; (2) more about the areal extent and variations of 

 specific ancient and modern strata, particularly those that are more or 

 less closely related to each other; and (3) more about the physics and 

 physical chemistry of the forces that affect sediments before, during, and 

 after deposition. Organized and coordinated efforts in these studies 

 should obviously bring forth many new facts and principles that would 

 be acquired slowly, if at all, by individual effort. 



Mechanical Analyses and their diagrammatic Eepresentation 



Studies of the mechanical constitution of sediment can be, and are 

 being, made by individuals, but the results are of little value because the 

 equipment and methods are not standardized. The work is handicapped 

 not so much because of the impracticability of a high degree of pre- 

 cision as for lack of equipment giving separates of approximately known 

 range in size that bear a uniform ratio to each other and constitute 

 analyses that are comparable. Proximate analyses made by an experi- 

 enced man are comparable Avith each other, but the results of two analysts 

 may not be comparable, unless the methods of the two are carefully 

 standardized at the beginning. For this reason it would seem desirable 

 to establish at first a single central laboratory where most collections 

 would be examined and reports made on them. 



What is the value of a mechanical analysis or of a set of mechanical 

 analyses? It depends, for one thing, on the care used in collecting the 

 material. The sample for each analysis should, to meet most purposes, 

 represent only a small fraction of an inch of thickness and should come 

 from an area of a very few square inches. The object is, of course, to 

 get grains deposited under one set of conditions. 



Aside from the determination of commercial values of deposits and 

 the furnishing of identification characters, perhaps the main value in 

 mechanical analyses lies in their promise of furnishing a record of some 



