part 1] DEPOSITS AT WORMS HEATH. 29 



with in the Rotherhithe Tunnel. This continued as a sarsen for a 

 considerable distance ; later on it contained a few small flint- 

 pebbles, then more and larger pebbles, finally passing into typical 

 Hertfordshire Pudding-stone. Small sarsens were also met with 

 in situ in the excavations for the Tube railway between the Angel 

 and King's Cross. This suggested that the hollow in which the 

 Blackheath Pebble-Beds had been deposited had been cut after 

 the sand had been silicitied into sarsen, the change taking place 

 soon after deposition. 



The occurrence of Clay-with-Flints beneath the Blackheath Beds 

 was important. So long as the Bullhead Bed \&y at the base of 

 the Beading Beds, no Clay-with-Flints was formed, as the base of 

 the Beading Series contained too much clay to let water pass 

 through. When the base was of a gravelly nature, the clay in the 

 overlying beds was washed down through the gravel, and filled 

 the interspaces between the flints left when the adjacent Chalk was 

 dissolved awaj r . 



Sir Henry Howorth said, with reference to the pipes, that it 

 was desirable that their full depth should be ascertained by boring 

 •or otherwise. He had never seen a really satisfactory theory of their 

 origin, although the discovery by Mr. JDavies of inclusions of 

 manganese, consistent only with a submarine origin, carried us 

 rsomewhat farther. It was clear, from the evidence given by 

 Mr. Whitaker, that the transport of the pebbles, at all events 

 in the filling of these pipes, took place after the Blackheath Beds 

 were laid down : how much later we were unable to tell. He was 

 -of the opinion that the concentric infillings must have been 

 introduced successively, each deposit in turn being however 

 eventually dischaiged, with the exception of a thin concentric 

 ribbon, which formed a fresh wall to the next comer. He 

 could not see by what process all this was done, nor how pipes 

 more than 30 feet deep could be emptied so methodically more 

 than once. 



Mr. A. L. Leach remarked that the sections at Worms Heath 

 exhibited most interesting effects of solution and subsidence. The 

 ^curious pittings or hollows noticed on many of the pebbles do not 

 seem to be caused simply by pressure, but by pressure combined 

 with a grinding motion, ■ and the pits are often quite fresh in 

 .appearance, as if due to movements recenth r or still in progress, 

 possibly movements of accommodation to changes of temperature. 



The grey discoid quartzites found in the pebble-beds serve to link 

 these deposits with the main area of Blackheath Beds in Northern 

 Kent. Similar quartzites have been found at Charlton, Hayes and 

 Keston Commons, East Wickham, and Bostal Heath. In the last 

 two localities, where they are fairly common, some scores have been 

 collected. They do not appear to resemble either the sarsens 

 found along the North Downs, or any of the sandstones in the 

 Lower Eocene deposits (Woolwich Beds) of Northern Kent. 



Mr. Walter Johnson said that he was interested in the revolu- 

 tionary doctrine which was propounded by Mr. Davies, and might 



