BLACKHEATH BEDS. 23 



Ft. 



London, Clay - - 20 



f Mottled plastic clay - - 23 



T i- Brown sand, clayey in parts 8 



Beds 1 ^ re y san d an d clay (impersistent) - 1| 



Pebble-bed passing down into green sand with green- 



4 coated flints - - 2 

 Chalk. 



On the west and north of the Colne several outliers of Reading 

 Beds occur beneath the glacial gravels, as for instance at Croxley 

 Green, but these cannot be shown on the map. 



At Ickenham, Ruislip and Pinner the formation consists 

 largely of mottled clay, and the same is true of the beds proved 

 by borings under the cover of London Clay over the greater 

 part of the area shown on Sheet 1. 



It should be mentioned that in Sheet 3 there is an unfor- 

 tunate error in the colouring. The numerous small outcrops, 

 coloured as ' Woolwich and Reading Beds ' in valleys cut through 

 the Thames river -gravels and in valleys between the gravel 

 terraces, are all London Clay, and are shown as such on the New 

 Series Maps of Windsor (269) and South London (270). The 

 only outcrop of Woolwich and Reading Beds in Sheet 3 lies 

 around Ewell and Sutton and has already been described. 



BLACKHEATH BEDS. 



This division is locally developed in the south-eastern and 

 eastern parts of the London District. 



It consists in the main of pebble-beds and sands, the pebbles 

 being almost wholly formed of flint, rarely of sarsen, and the 

 sand of quartz with some flint chips and heavy minerals. They 

 are occasionally cemented by calcareous, ferruginous, or siliceous 

 matter, forming a conglomerate. 



Originally grouped for the most part with the Basement Bed 

 of the London Clay by Prestwich, the pebble -beds and sands 

 were separated in 1866 by Mr. Whitaker and designated the 

 Oldhaven Beds from a locality between Herne Bay and Reculvers. 

 Subsequently he applied the term Oldhaven and Blackheath 

 Beds, the eastern type being sandy and the western pebbly, but 

 for purposes of local designation in the London District the latter 

 name only is used. The beds rest irregularly on the Woolwich 

 and Reading Series, locally cutting through many layers even 

 down to tho Thanet Beds ; while to the south the beds transgress 

 on to the Chalk near Caterham and Worms Heath and also at 

 Knockmill, as shown in the extreme south-east corner of the 

 map, and thus have derived flint to form pebbles directly from 

 that formation. 



The fossils of the Blackheath Beds include estuarine, marine, 

 and freshwater shells ; and among the various forms relation- 

 ship can be traced with species of the preceding Woolwich and 



