CLAYGATE BEDS. 29 



Sand ; the clay predominates in the lower, the sand in the upper 

 part. The passage beds were shown by a separate colour on 

 Mylne's Geological Map of London in 1856, but Prestwich 

 regarded them as part of the London Clay and on maps subse- 

 quent to Mylne they have been included with that formation. 



Mr. Whitaker noted 1 their occurrence around London and 

 considered them as true passage beds. He called attention to 

 their presence at Wimbledon, Norbiton, Gipsy Hill and north 

 of the Crystal Palace, and quotes Caleb Evans's 2 account of 

 them at Hampstead and Highgate. 



In the first edition of the present Memoir H. B. Woodward 

 drew attention to the anomalies that result from inconsistency 

 in drawing the boundary between London Clay and Bagshot 

 Sands, and adds that ' in a future 6-inch survey the passage -beds 

 will no doubt be separately mapped ' (p. 36). That has now 

 been done over the greater part of the area here considered, 

 though Essex, where there is a large outcrop of these beds, has 

 not yet been re-surveyed. The necessity for separating these 

 passage-beds from the London Clay has recently been illus- 

 trated. The great reservoirs at Staines were excavated in 

 Thames gravels down to the underlying London Clay, which 

 formed an impervious bottom. Further reservoirs have been 

 proposed near Littleton, south-east of Staines, but here trial 

 borings revealed the fact that the beds, shown as London Clay 

 on the Old Series Maps, contained seams of sand and would not 

 retain water. These beds are described in the Windsor and 

 Chertsey Memoir as ' Claygate Beds.' This name was given by 

 Mr. Dewey because the passage beds are well developed and have 

 long been worked for bricks and pottery at Claygate in Surrey. 



At this type -section these beds have up to the present yielded 

 no fossils ; consequently, we are unable to correlate them with 

 fossiliferous horizons elsewhere. Until more detailed work is 

 done on the zonal distribution of fossils in the London Clay it 

 will be impossible to say what horizons they represent. At 

 Willesden Green 3 there are beds which on account of their litho- 

 logical character are referable to the Claygate Beds ; immediately 

 beneath them is a layer of septaria which has yielded many shells 

 and also abundant plant-remains. The shells include Protocardia 

 nitens (J. Sowerby) and Teredo antenautce J. Sowerby in abun- 

 dance; the heart-shaped sea-urchin Hemiaster branderianus 

 Forbes has also been found here. Additional records of fossils 

 from this locality have been noted by Mr. Wrigley. 4 In similar 

 beds at Shooters Hill 5 Mr. A. L. Leach records Cyprina morrisi 

 (J. de C. Sowerby), Pectunculus decussatus J. Sowerby and other 

 shells, found in ferruginous boxstones. 



1 ' Geology of London ' (Mem. Geol. Surv.}, vol. i, 1889, pp. 238-265 



2 ' Geology of Hampstead,' Proc. OeoL Assoc., vol. iii, 1873, pp. 21, 22. 

 } ' Summary of Progress for 1914 ' (Mem. Geol. Surv.), 1915, p. 30. 



* Proc. Geol. Assoc., vol. xxxii, 1921, pp. 139-140. 

 5 Proc. Geol. Assoc. t vol. xxiv, 1914, pp 115-117. 



B 2 



