30 LONDON DISTRICT. 



The ' boxstones ' seem to be a constant feature ; they are 

 ' hard concretions of ferruginous loam, enclosed usually by 

 harder and more ferruginous shells of limonite.' The septaria 

 or cement-stones of the London Clay are absent, but pyrites 

 nodules and crystals of selenite not uncommon. 



At the type locality the following section was observed in 

 Sims & Sons' brickyard in 1911 : 



Ft. 

 f Sand, yellow and current-bedded, with a thin seam 



ags 



Claygate 



I Ironstone, at times only ferruginous clay - -12 



Pipe clay and white sand in alternate layers - 1 



Pure white sand ,].- 



White sand and grey pipe-clay in alternate bands, 



some beds of sand an inch thick - -4 



Ironstone nodules enclosing white sand or clay - 



Beds. 



Pure white sand up to 



Clay, grey and lilac, alternating with white sand up to 



5 ins. thick - 3 



Sand and clay, drab or lilac 

 Purplish-brown clay, evenly bedded in 2 to 4 in. seams 



with narrow veins of sand - 30 



London Clay. Clay, blue or dark grey-green, enclosing nodules of 

 pyrites, claystone concretions and septaria, often 

 fossiliferous - - 20 



The lilac tint is characteristic, and as it is not easily lost by weathering 

 forms a useful guide in the field. 



A good natural section may be seen in the cliff of the River 

 Mole at Westend Common, showing 35 ft. of white or buff sand 

 and drab or lilac clay in alternating bands up to one inch in 

 thickness ; fragments of leaves are common here, but badly 

 preserved. 



Claygate Beds underlie the gravel at Coombe and the southern 

 part of Wimbledon Common. 



In the north-west Claygate Beds occur at Harrow, but 

 sections are scarce ; the outlier at Willesden Green is mentioned 

 above and many accounts of the beds at Hampstead and High- 

 gate, notably those in the Archway cutting, have been published, 

 for the most part many years ago : a summary of the chief points 

 has been made by Mr. Whitaker. 1 The important paper by 

 Caleb Evans quoted above includes a map of Hampstead 

 showing the Claygate Beds, which form a continuous mass 

 extending round Highgate, capped by the outliers of Bagshot 

 Sand. The section proved in the Tube Railway shaft at Jack 

 Straw's Castle, Hampstead, seems to show, under 4 ft. of soil 

 and gravel, 16 ft. of Bagshot Sand and 110J ft. of Claygate Beds 

 on London Clay. Other small outliers have been detected at 

 Horsenden Hill and at Hanger Hill, Baling ; these will all be 

 shown on the forthcoming North London Map (Sheet 256) and the 

 latter is indicated on the Special London Sheet 1 as ' Valley 



1 ' Geology of London * (Mew. Geol. Surv.), vol. i, 1889, pp. 256-258. 



