97 



accounting for the matter by the action of land ice ; 

 because the Woolwich shell beds are found to the 

 South on the hill-top above, and traces of their passage 

 may be detected along the whole interval between the 

 two places, which is marked by a shallow depression ; as 

 the London clay once capped the same spot, it is that 

 which is now found among the Brickearths. 



About a mile and a half westward is still a small 

 outlier of London clay, and traces of its degradation may 

 be detected in several places as trail, over the pebble beds 

 and Thanet Sand on Northumberland Heath, on its course 

 towards the Thames. It often presents the appearance of 

 a blue clay, sometimes yellow, full of slickensides, and 

 occasionally contains crushed masses of chalk, the nodules 

 of .which are hard. It is this which Mr. Tylor in his 

 description of Erith brickpit above mentioned has called 

 rolled chalk, and has described as mixed with clay, and 

 resembling Till or Boulder clay, which it does ; but the 

 rolled appearance is I think produced by solution of the 

 edges. In a section I had made in Mr. Petman's nursery 

 garden there was — 



Made soil and v. s. . . . . ift. 3in. 



Trail of Eocene pebbles .. .. — Sin. 



Clay, yellow and blue, with chalk 3ft. oin. 



A pan of tufa, formed from dissolution 



of chalk . . . , . . — 6in. 



Oldhaven pebbles . . 



In the Uphall pit at Ilford I saw formerly several 

 well marked masses of true boulder clay — undoubted in 

 that situation — enveloped in brickearth, and as at Erith, 

 London clay remanie was also observed. 



The heavy mass of trail on its arrival at the edge of 

 the river doubtless broke down the cliff and thus produced 

 the landslip of Mr. Whitaker, but whose origin is glacial. 

 On tracing some of these heavy masses of disturbed strata 

 further up the bed of the river, they are- seen to contort 

 the Brickearths and gravels at a lower level than the last 



