464 H. A. Baker — Loose Arenaceous Sediments. 



been done, the writer could discover no trustworthy case in which 

 the work had been accompanied by accurate determination of the 

 mean diameter of the material used in the experiments. Dr. John 

 S. Owens/ however, made observations in the case of phenomena 

 of type (6) above, and it was found possible to make use of his 

 results. He carried out experiments on the transporting power 

 of sea-currents, using flint pebbles ranging in diameter from half- 

 an-inch to six inches. The pebbles were rolled by the currents 

 over a sand surface. As a result of his experiments, Owens arrived 

 at the formula : — 



45F^ 

 F — 64 

 where d = diameter of pebble in inches 



W = weight of a cubic foot of pebble material in pounds, 

 V = velocity, in feet/sec. of current just competent to 

 transport the pebble. 



Now it seems legitimate to argue that, where we have flint pebbles 

 scattered throughout a bed of sand we may fairly assume that the 

 same conditions were required for the deposition of the pebbles as 

 for the sand. The observations of Owens, Vaughan Cornish, Gilbert, 

 and others, have, however, shown that when arenaceous material 

 is under transport by currents of lower velocity than 2-5 feet per 

 second it invariably moves forward in the form of sand-ripples, and 

 the rippled surface always arrests the movement of pebbles unless 

 the velocity of the current is greatly in excess of that required to 

 move them. According to the formula given by Owens, at a speed of 

 25 feet per second, a current would be able to transport flint pebbles 

 up to 2-85 inches in diameter. Therefore, where we have a bed of 

 sand with flint pebbles scattered fairly uniformly through it, and 

 these pebbles clearly average less than 2"85 inches in diameter, we 

 may assume that the current which transported the material to its 

 present resting-place, and from which it was deposited, was at least 

 as fast as that required to transport pebbles of the size seen, since 

 the arrest and burial of these pebbles was probably brought about 

 in consequence of the formation of sand-ripples on the bed. We 

 may assume further, that the velocity of the current was not greatly 

 in excess of that required to move pebbles of the size seen, for, had 

 it been so, the sand-ripples would not have checked the pebbles in 

 their career. 



The Thanet Beds contain no flint pebbles, but after some search 

 the writer selected a section in Blackheath Pebble Beds in which 

 numerous flint pebbles, averaging less than 2-85 inches in diameter, 

 but of notable uniformity of size, were evenly distributed through- 

 out a bed of sand. A sample was taken containing both pebbles and 

 sand. One hundred representative pebbles were selected and their 



' Owens, "Experiments on the Transporting Power of Sea Currents": 

 Geog. Journ., April, 1908, pp. 415-20.* 



