LABORATORIES AND EQUITMEKT 417 



others, for example, among the Florida Keys, by Louderback and others 

 in San Francisco Bay, and that by the Bureau of Fisheries constitute 

 excellent and very full preliminary requisites and fall barely short of 

 areal surveys. One can scarcely foresee the nature and value of the re- 

 sults of well organized expeditions that have such surveys as their primary 

 object. 



Laboratories and Equipment 



Since one of tlie main fields of laboratory work will probably be me- 

 chanical analyses, and since there is a peculiar need for standardization 

 of such analyses, it would seem desirable to plan for one central fully 

 equipped establishment. ^lore or less laboratory work can, of course, be 

 ])rofitably undertaken anywhere, but a recognized leader would bring 

 about a rate of progress that would not otherwise be realized. After 

 standards are well established, it may be that all kinds of work can be 

 carried on profitably at various independent places, but at present the 

 great need is for standardized screens, standardized centrifuge, and stand- 

 ardized microscope work. Most tests made with commercial screens are 

 worth little (1) because only the number of wires to the inch is kno^vn, 

 (2) because in many screens the wires are not uniformly spaced, (3) be- 

 cause different methods will give widely different results with the same 

 set of screens, and (4) because the sizes of openings in the successive 

 screens do not bear a fixed ratio to each other. 



It would be relatively easy to devise for sands and gravels a standard 

 set of field screens that would give results of fair accuracy. The principal 

 shortcoming would arise out of differences in method of use, but this 

 might be largely obviated by screening directions. Whether the openings 

 should be round or square has not been settled to the satisfaction of all, 

 but in any case they should certainly bear a fixed ratio one to another, 

 and this ratio should be some root of 2 or 10. 



Some of the Problems 



Among the problems awaiting attention are many concerning the 

 source and destiny of eroded materials. Sometimes we know not whence 

 the deposit came. For example, the Pottsville formation of southern 

 Illinois is thick and contains quartz pebbles. Does this prove orogenic 

 movement and near-by mountains? There is almost certainly no ade- 

 quate source for the pebbles within hundreds of miles. 



Again, the Mississippi Valley loess is commonly thought to have come 

 from the floodplains of the Mississippi and some of its tributaries, but 

 preliminary computations indicate that the volume of the loess is too 



XXIX— Bull. Geol. Soc. A.m., Vol. :M, 1019 



