466 



H. A. Baker — Loose Arenaceous Sediments. 



(2'211 cm. as compaxed with 2'197 cm.), and the Equivalent Grade 

 of the associated sand similarly gave a figure extraordinarily near 

 that obtained in the case of the first sand ("lOG mm. as compared with 

 •102 mm.). If this be not a singular coincidence it must indicate 

 a significant connexion between the size of the pebbles in a sandy 

 bed and the Equivalent Grade of the sand itself. With regard to 

 the considerable variation often to be seen in the sizes of pebbles 

 included in a sandy bed, it should be borne in mind that the weight 

 of stone which a current can move varies as the sixth power of the 

 velocity, and that therefore a slight increase in velocity may produce 

 effects out of all proportion to what woidd be expected. The 

 determination of h from the data of the second experiment 

 gave '056 as compared with "054, the value obtained previously, 

 and accordingly "055, the mean of these two results, was taken. 

 Hence, for the case of the transport, in bulk, of arenaceous material 

 similar to that of which the Lower London Tertiary strata of the, 

 southern side of the London Basin are composed, the formula 



c? = .055 7/ 

 where d is the Equivalent Grade of the material in mm. and F^ 

 is the velocity in feet/sec. just competent to transport the material, 

 is put forward with a certain amount of confidence. 



Uppek Thanet Beds. 



^ The highest Thanet Beds seen at Pegwell Bay really represent a fairly low 

 level in the deposit, but these data are included here because they were used 

 in the diagram (Fig. 8). 



