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NOTES UPON SOME MOUNDS NEAR THE
ESTUARY OF THE THAMES.
By J. G. GOODCHILD, F.G.S., F.Z.S., H.M.'s Geological Survey.
[Read February 27th, 1886.]
The curious mounds that occur here and there in the fluvio-marine
alluvial tracts of Essex have been explored time after time by several
competent observers without, so far, ever having yielded evidence
that would enable one to arrive at any satisfactory conclusion regard-
ing their precise nature and origin. Mounds externally similar and
occurring under much the same conditions have long ago been
known to exist elsewhere. The nature and origin of these has also
been again and again discussed with much the same kind of result
as was arrived at in the case of the estuarine mounds of Essex.
With a view to throwing at least a little additional light upon some
of the questions still undecided, I undertook, at the suggestion of the
President of the the Essex Field Club, a re-examination of some of
these mounds occurring on the south side of the Estuary of the
Thames, where their external form had often attracted my attention
at intervals since the year 1860. The area where these mounds
occur in greatest number appears to be the low marsh land of Sheppey
bordering upon the Swale and the Medway. The marsh land referred
to is a broad expanse of alluvium occupying the low ground between
the foot of the slope extending Thames-ward from the North Downs,
and the mass of London Clay forming the uplands of Sheppey. The
marsh alluvium of Sheppey appears everywhere to be spread over a
very uneven floor, which seems to consist entirely of London Clay.
The irregularity of this floor is clearly shown by the fact that here
and there, all over the marsh, detached bosses and small hills of
London Clay rise above the dead level of the surrounding marsh,
and are separated from each other, and from the main mass of
Sheppey, by intervening flats of alluvial clay of variable extent. The
origin of these particular mounds hardly admits of any reasonable
doubt: they are simply what Mr. F. C. J. Spurrell1 has aptly termed
"leavings" of London Clay, and are clearly due to the irregular
denudation of the thickness of London Clay that formerly spread
continuously over this and the area adjoining.
Associated with these, however, are some other mounds, generally
smaller in size, whose nature does not so readily admit of explana-
1 "Early Sites and Embankments on the Margins of the Thames Estuary," "Archaeological
Journal," vol. xlii., p. 269.