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 Pevéle, 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 /imon 
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. 
