100 



PROF. MOEEIS — GEOLOGY OF THE LONDON l^ASIN 



northern Chalk lands compared with the open downs of uncovered 

 (Jhalk on the southern side of the Thames.* 



Overlying the Woolwich beds in some parts of the London 

 Basin, but apparently not found in this district, are pebble beds 

 and sands, of variable thickness. Tliese have been termed by Mr. 

 Whitakcr the Oldhaven and Blackheath Beds ; their molluscan 

 fauna is both estuarine and marine, and is somewhat related to 

 the beds below and the London Clay above, of which latter forma- 

 tion these beds have been considered the base. These perfectly 

 rounded pebbles, like those of the Woolwich beds below, are so 

 well marked that they can be readily detected amongst the mass of 

 superficial gravels of later age spread over the district. Their 

 nature and form indicate that they were derived from the Chalk, 

 and rolled upon some shore for ages, having been subsequently 

 spread over a larger area (far perhaps from their parent source) 

 by the changes to which the sea or estuarine bed was subjected. 



Fig. 5. — General Section on Raihvay, Bushey Cutting. 



(") London Clay feet. 



\b) Basement-bed of the London Clav, with numerous fossils 5 ? 



/ [g) Sands " 3 ? 



\ {h) Mottled clays with a few beds of sand 35 



Rnadinr^ Beds, i («) Saud nearly white, with a few layers and patches 



of flint-pebbles 10 



\ (/) Shingle bed of Hint-pebbles in ochreous sand ... 15 

 («)) Chalk. 



After the deposition of these estuarine bods, the gc^ology of the 

 TiOndon area shows that another physical cliange took place, pro- 

 bably of still greater interest. The Woolwich Beds indicates mode- 

 rately temperate conditions ; but the overlying stratum — that wliich 

 is known as the London Clay — presents a very diil'i'rent character : 

 firstly, with regard to its mode of accumulation ; and secondly, as 



* "The chalk hills which bound the T.'rtiary area on the north, unlike tli 

 chalk of Salisbury I'lain, present but a snudl extent of open downs, aiul ar 

 well wooded on tiieir summits. This arises in part from a eovering of cla 



