H. A. Baker — Loose Arenaceous Sediments. 



417 



is that if this be done for a series of localities, the series of straight 

 lines obtained show a strong tendency towards parallelism. (See 

 Fig. 7.) This signifies that in the case of the Thanet Beds there is 

 a tendency towards a simple linear relation between change of 

 Equivalent Grade and change of Grading Factor. On investigating 

 this point the writer was able to obtain the following remarkable 

 result connecting two samples of the Thanet Beds : — 



If sample 1 has Equivalent Grade E^ and Grading Factor G^ 

 and sample 2 has Equivalent Grade E^ and Grading Factor G^, 

 then (?2 = ^1 ± 2-56 {E^ - E,). 



Take + sign when E^ > E^ and — sign when E^ < E^. 



Fig. 7.- 



•oi -oa -oj -o^ -OS -ob -oy OS" -ccj ./ ./( ./i ./3 .,j^ ./j- 



-Graph showing the relation between Equivalent Grades and Grading 

 Factors of Thanet Beds material from various localities. 



This evidence of steady change in the lithological character of the 

 sediments with concomitant change in the degree of sorting of the 

 material signifies the establishment of conditions under which more 

 and more highly sorted material was being deposited. The degree 

 of sorting of a sediment is probably, in general, a cumulative effect 

 depending upon the total vicissitudes through which it has passed, 

 and these vicissitudes are greatest in the case of material which, 

 originally derived from the denudation of a land-area, has passed 

 successively through the stages of having been incorporated in 

 fluviatile and estuarine sediments and has finally been deposited 

 under marine conditions. In the striking feature of the Thanet Beds 

 to which allusion has been made, we have, perhaps, the sign of the 

 gradual and definite establishment of marine conditions. 



VOL. LVII. — NO. IX. 



27 



