CHAP. XI.] HANTONIAN PERIOD. 221 



should be thickest across the middle part of the London 

 basin. The Hertfordshire conglomerate or pudding-stone 

 is a relic of one of these beds ; another is to be seen at 

 Lewisham, and the Blackheath Beds form an enormous 

 mass of shingle at a higher horizon. 



If these pebbles had been brought by a large river from 

 the west or south-west, we should expect to find them 

 thickening in those directions ; but such is not the case, 

 they actually thin out westward as well as eastward, and 

 appear to be local deposits confined to the northern side of 

 the Wealden anticline. Mr. Whitaker has remarked that 

 the pebbles in the Blackheath Beds are always well worn 

 and rounded, and he infers that they were not formed as a 

 beach against a shore-line, for in such beaches there are 

 generally a certain number of subangular pebbles, but he 

 thinks they have been carried out some distance from the 

 actual shore, and only brought to rest after a long exposal 

 to the wearing action of waves and currents. This is 

 exactly what would happen under the geographical con- 

 ditions I have supposed. It is, however, quite possible 

 that many of the pebbles were rounded in the channels of 

 small rivers draining the Chalk island of the Weald 

 before they were brought down to the shores of that 

 island. 



The freshwater beds of the Woolwich group, again, were 

 clearly formed in the estuaries and deltas of small rivers, 

 and there is no reason whatever for supposing that these 

 rivers came from the west, but much reason to think that 

 they drained a tract of land over the Wealden area. 1 They 

 only occur over a limited space on the northern and 

 southern sides of this area, and they are just such deposits 

 as might be formed in lagoons and in the estuaries of 

 rivers which drained into a land-locked bay. Moreover, 

 Professor Prestwich states that the prevailing dip of the 

 1 See Prestwich, " Quart. Journ. Geol. Soc.," vol. x. p. 135. 



