3^0 



it. A. Baker — Loose Arenaceous Sediments. 



The Equivalent Grade of this sediment is identical with that of 

 the first, viz. "059 mm., but the two curves are not identical. It can 

 be seen at a glance that the first sediment shows greater variation 

 than the second, and hence the latter yields a higher Grading Factor, 

 the value in this case coming out at "693. We see, then, that the 

 Equivalent Grade of a sediment together with its Grading Factor 

 afiord a pair of values unique for any sediment. 



It should be remarked that in selecting sediments to serve as 

 illustrations of the utility of these two factors, the writer has 

 deliberately chosen examples in which the differences in mechanical 

 constitution are by no means great. In general, arenaceous sediments 

 show very much greater differences in mechanical compiosition than 

 are to be observed in the examples selected. If, then, comparatively 

 insignificant differences can be indicated by the methods of treatment 

 here outlined, how much more apparent become the greater 

 differences very generally found. 



When the data yielded by mechanical analyses of sediments have 

 accumulated sufficiently, it should be a simple matter to draw up 

 a scheme of classification, according to mechanical constitution, 

 for the loose detrital sediments, based upon determined values of 

 Equivalent Grades and Grading Factors. The determination of 

 the values of these factors in the case of those sediments which are 

 used in the industries can hardly fail to be of great utility. The 

 importance of mechanical constitution in the case of glass sands 

 and in the case of the refractory sands used for furnace and foundry 

 purposes has already been clearly demonstrated by Professor 

 Boswell. But from the purely geological point of view there is every 

 reason to believe that from the detailed study of the mechanical 

 constitution of the loose detrital sediments of the geological column, 

 much light will be thrown upon many obscure questions, especially 

 in reference to conditions of deposition of sediments. When 

 palaeontological evidence fails, the stratigrapher is thrown back 

 upon the lithology of the deposits, and in the case of a loose, 

 arenaceous sediment the lithological evidence is very strongly and 

 helpfully augmented if the elutriation-curve be available. 



(To be continued. 



