the Upper and Lower Drift of the Eastern Counties. 403 



gravel-beds overlying the chalk, and also the detached Tertiaries 

 on the English side of the British Channel — beds which I regard 

 as wholly of newer date than the valleys, and consequently of 

 newer date than either of the beds forming the subject of this 

 paper. Of the lowermost of the latter beds, I have shown that 

 its margin crossed the centre of Essex ; but that portion of the 

 upper Drift which in England is known as the Boulder-clay, I 

 believe, originally extended continuously over the area south of 

 the Thames, and was the more oceanic portion of that part of 

 the upper Drift which formed the Loess of Belgium — and 

 that the same formation spread over northern France. No 

 remnant, however, of this upper bed, south of that at Muswell 

 Hill, six miles north of London *, has, so far as is yet known, 

 survived the denudation, which removed not only that bed, but 

 large areas of the Eocene beds also ; so that the gravel-deposits 

 crowning the surface of the denuded Chalk and Tertiary on the 

 English side of the Channel are in no way connected with either 

 of the beds which form the subject of this paper. 



In this uncertainty attending the spread of the upper Drift 

 over France, I have not attempted to pursue the correlation 

 of the deposits beyond Belgium ; but it is apparent, from the 

 views I take, that I regard the limon des plateaux which caps the 

 chalk heights overlooking the valley of the Somme, and which 

 Sir Charles Lyell seems inclined to refer to the Loess, as of a 

 later date than that deposit, although I believe it to differ in age, 

 as Sir Charles justly points out, from the deposits filling the 

 Somme valley. According to my views, the whole mass of the 

 Eocene tertiaries that spread from Mons en Pevele, on the 

 north, to Beauvais on the south, were denuded from the chalk 

 forming the heights of the Somme, subsequent to the deposit of 

 the Boulder-clay over those Tertiaries, and before this limon 

 des plateaux had settled upon the surface of the chalk thus 

 exposed. 



The Boulder-clay of the east of England has hitherto, so far as 



* Over the London Clay north of the Thames, and particularly over 

 the south-east of Essex, stones occur not unfrequently on the surface of 

 the soil, that never came from the wreck of the Eocene tertiaries, but well 

 agree with those included in the Boulder-clay : these I believe to have 

 come from that deposit, and, having escaped the transporting agencies in 

 operation at the time of the denudation, to have settled on the denuded 

 surface of the London Clay, and in that way now convey a faint indica- 

 tion of the former existence of the Boulder-clay over the area where they 

 are distributed. A boulder of crystalline rock, water-worn, containing 

 several cubic feet, exists at Grays, and another at Benfleet ; but as they 

 may possibly have been brought by ship, it would be unsafe to rely on them 

 as evidence of the Boulder-clay having extended, as I believe it did ex- 

 tend, over those places. 



