30 THE SECTIOX AT WORMS HEATH. [vol. lxXV,. 



ultimately be proved correct, to the effect that the Bullhead Bed 

 had not been formed in position, since it required the agency of 

 sea -water to produce the green coat. The suggestion that the 

 London Clay was already being deposited in the deeper parts of 

 the London Basin at the time when the Blackheath pebbles were 

 being heaped up, helped to solve several difficulties. With respect 

 to the pebbles themselves, whence were they directly derived ? 

 The older Tertiary deposits could not have afforded enough material,, 

 while, contrariwise, the Blackheath Beds may have aided in 

 supplying some of the Bagshot Series : then we must look to the 

 Chalk. It is agreed that the Chalk originally supplied the flinty 

 material ; but, in order to gain the present degree of roundness, the 

 pebbles must have travelled a great distance. Patches of the Black- 

 heath Beds are found right up to the Chalk escarpment, and even a 

 little beyond. Could Mr. Whitaker suggest where the Chalk shore- 

 line, during the early stages of the deposition, was approximately 

 situated ? The speaker was of the opinion, formed from personal 

 inspection, that the cmartzite- pebbles were rather more numerous 

 at Worms Heath than had been allowed for in the paper. 



Mr. A. J. Bull said, in regard to the suggested identity of 

 sarsens with the quartzites of the Blackheath Beds, that he had 

 found them to differ petrologically. The grey quartzite consists of 

 quartz-grains with a small amount of siliceous cement, although in 

 places it may be a clear quartz-mosaic ; while, in the sarsens, the 

 quartz-grains are separated angular fragments of very variable size, 

 held together by a fine-grained cement or ground-mass which is 

 largely siliceous. The great disparity in the sizes of the grains in 

 the sarsens can readily be detected with a pocket-lens on the 

 fractured surface of a hand-specimen. 



Mr. C. E. N. Bromehead expressed interest in the horizontal 

 and vertical distribution of the Blackheath Pebble-Beds. Hori- 

 zontally they appeared to form a great crescent made up of 

 individual crescentic banks of pebbles, somewhat resembling a series 

 of sand-dunes. The crescents were convex to the east. On this 

 outer side were the marine Oldhaven Beds, on the inner western 

 side the Beading Beds. Immediately in the lee of the crescents 

 the freshwater bed of the Woolwich Series was found, suggesting 

 the formation of freshwater lagoons protected from the sea by the 

 pebble -ridges. 



In the vertical sequence he did not think that they marked a 

 definite horizon, but were contemporaneous with various members 

 of the normal Tertiary sequence. At the type-locality the Black- 

 heath Beds occur almost at the base of the Woolwich & Beading- 

 Series, only the 'Bottom Bed' being present beneath them, whereas 

 at other points nearly the whole normal sequence was found, and 

 the Pebble-Beds come in at the top ; locally, they might even be 

 contemporaneous with the lower part of the London Clay. 



The Pebble-Beds in the higher division of the Eocene were 

 similarly impersistent, as, for instance, that at the base of the 

 Barton Sands. At Stanners Hill, between Virginia Water and 



