86 LONDON DISTRICT. 



Upminster on the northern side of the Thames ; and at Claygate, 

 Xorbiton, Norbury and elsewhere on the southern side. 



The Bracklesham Beds were worked for brickmaking to the 

 south-east of Weybridge Station, and west of Woburn Park, 

 Addlestone. 



SAND. 



The Thanet Sand mixed with clay has been used in pottery 

 work and brickmaking ; but this formation is noted as yielding 

 the finest moulding material for iron and brass foundries. Indeed, 

 Mr. Whitaker has remarked that the occurrence of this good 

 foundry sand is said to have determined the site of Woolwich 

 Arsenal. It is now largely worked at Erith (p. 18), whence it 

 is exported to the North of England and various parts of 

 Europe. 



Mixed with ashes and sharp sand the Thanet Sand has also 

 been used in the preparation of mortar. 



Some of the Tertiary sands have been found serviceable for 

 glass-making, and recently the Thanet Sand at Beddington has 

 been utilized in the manufacture of silica-lime bricks. At that 

 locality, to the south-east of St. Mary's Church, there are 

 extensive underground workings or c caves ' of unknown anti- 

 quity in the Thanet Sand. Some small isolated chambers in the 

 Thanet Sand near Waddon House, Croydon, have been described 

 by Clinch as probably places of burial during later Neolithic 

 times. 1 



Grey and brown sand at the base of the Blackheath Beds at 

 Addington has been dug for sale as ' silver sand.' 



Sand for mortar is obtained in many places from layers in 

 the Thames Valley gravels. 



GRAVEL. 



Gravel has been dug from very early periods for making and 

 mending roads and path-ways, mostly from the Valley gravels, 

 and the higher Plateau gravels. Sometimes the Eocene pebble- 

 beds have been so utilized, but these and the more pebbly 

 Plateau gravels are now more worked for concrete than for 

 road-making. Under London there exist numerous excavations, 

 now filled with made-earth or rubbish, from which the gravel 

 was extracted; in more recent excavations in the central area, 

 gravel is dug out for the purpose of carrying foundations of 

 buildings into the London Clay. 



The Kensington gravel-pits were famous early in the last 

 century. At the present time among the more extensive pits, 

 where the gravel is more than 40 ft. thick, are those of Dartford 

 Heath, where different varieties are obtained for pathways, for 

 ballast, etc. Other large pits are worked at Hanwell. 



1 Trans. Croydon Nat. Hist. Soc., 1902-3. 



