Maryland Geological Survey 129 



An examination of the diagrams on p. 170 leads to the recognition of the 

 following general effect of different conditions and agents on the diagrams. 

 Most conspicuous is the difference in the degree of sorting or sizing. The 

 most complete sizing is produced by strong waves and by wind action 

 (p. 170, figs. A, C, J, K, L). Off-shore marine sediments (p. 1T0, 

 fig. C) are as well sorted as beach sands, differing only in having the 

 maximum in a finer size. A similar difference in the maximum appears 

 between dune sands of temperate regions (p. 170, fig. J) and those of 

 tropical regions (K, L), and though this might be due to a difference in 

 the part of the dunes from which the different samples were taken, it is 

 also quite possible that the prevailing winds of these tropical regions are 

 stronger. 



But while the deposits found respectively under the influence of winds 

 and of strong waves thus agree in their perfection of sizing, they also 

 show a certain difference in that, in the product of wave action, after the 

 maximum the largest portion is the next finest material, while in the 

 eolian deposit the next coarsest is generally the largest. 1 



The lagoonal deposits may be taken as representing in general deposits 

 in a small body of water in which there is much weaker wave-action and 

 less room for the horizontal separation of sizes than in the ocean. Conse- 

 quently sizing is less perfect (p. 170, figs. F, F ) . 



Eiver sediments in addition to being poorly sized tend, as explained by 

 Mohr, = to show an abrupt rise of the curve on the left and a gentle fall 

 on the right. That is, sedimentation of streams is likely to take place 

 from a sudden change in velocity ; hence all of the coarsest and much of 

 the finer material that it has been able to carry to the point of sedimenta- 

 tion will suddenly drop out. This is well illustrated by the typical dia- 

 gram, M, p. 170, 



Delta deposits show a combination of this stream effect with a certain 

 amount of sorting as can be seen in diagrams I) and I, pi. II, but the sort- 

 ing effect of wave action appears very rapidly away from the edge of a 

 marine delta. 3 



1 See further, Udden, J. A., The mechanical composition of wind deposits. 

 Augustana Library Publ. No. 1, 1898. 



2 Mohr, E. C. Jul., Ergebnisse mechanischer analysen, etc. (op. cit. ) , p. 35. 



3 See some of the analyses in Thoulet's study of the Gulf of Lyon, cited 

 above. 



