CHAP. XI.] HANTONIAN PERIOD. 201 



The pebble beds which form such a marked feature in 

 the district to the south-east of London lie principally 

 above the main mass of the Woolwich clays and sands. 

 Eastward they appear to pass into marine sands with a 

 pebbly base, and they have been described by Mr. Whitaker 

 under the name of the Oldhaven and Blackheath Beds. 

 He has also shown that during their formation erosion 

 took place on an extensive scale, and that these pebble 

 beds sometimes cut through the whole of the underlying 

 Woolwich Beds, so as to rest upon the Thanet Sands. 

 Moreover, it seems probable that they extended beyond the 

 limits of these sands to the southward, overlapping them 

 and resting directly on the Chalk, just as the Woolwich 

 Beds do to the westward. 1 



The very existence of such accumulations of flint pebbles 

 to a thickness of 40 or 50 feet in some places would lead 

 us to infer that they have been derived directly from the 

 Chalk, and consequently that part of the Chalk area lying 

 to the south of the London basin was then exposed to 

 erosion. 



The London Clay and the so-called Lower Bagshot Beds 

 may be considered together, for there is much reason to 

 think that they are parallel formations, and that the sands 

 replace the clays towards the west and south-west. The 

 London Clay is a marine deposit, formed during subsidence 

 in the deeper part of a shallow sea. Its basement bed is 

 always sandy and pebbly, but the mass of the overlying 

 deposit in the eastern districts is clay. It would appear, 

 however, that the lower and middle parts of this clay 

 were formed in deeper water than the upper, or Sheppey 

 Beds, which only yield fossils of terrestrial origin, trans- 

 ported by rivers, namely, the fruits, seeds, and leaves of 

 plants in great abundance, together with occasional bones 

 of snakes, birds, and other terrestrial animals. The Lower 



1 See " Quart. Journ. Geol. Soc.," vol. xxii. p. 419. 



