WELLS ON FOWLNESS ISLAND.
125
formations. In the latter respect, the further value lies in
showing that the Fowlness wells derive their supply from the
Lower London Tertiaries, and not from any subordinate sand
bed in the London Clay ; that the base of the London Clay is
only 300 feet below Ordnance Datum at Church End, as at
Burnham and Southend; and that the Chalk might there be
reached at - 450ft. Therefore, the — 400ft. Chalk-contour of the
map referred to must be altered to sweep round from Prittlewell
through Barling to the mouth of Broomhill in the Crouch, and
so out to sea ; the — 500ft. line from North Shoebury through
Great Wakering, and along the southern margin of Fowlness ;
and the — 600ft. line well out on the Maplin Sands, unless the
synclinal between Essex and Thanet flattens too rapidly for the
600ft. to be reached. Possibly the 564ft. of Shoebury may be
the limit of the depth obtained by the Tertiaries.
Mr. C. Harvey told me, some 40 years ago, that at the Quay
Farm a thick bed of blue salt mud or silt separated the surface-
clay from the clean sand below. I had inclined on this basis to
conjecture that Mr. Gibson was the tenant of the Quay when the
well in question was sunk in his yard, as the record fairly meets
Mr. Harvey's description. The Broomhill or Quay Reach pro-
bably held originally a more easterly course from Whitehouse,
its Fowlness bank lying over 1,000 yards from the present line.
The remains of the old wall still rise above the general level,
and under the vanished kiln of the former brickyard at this
point, occurs clean tawny clay with sandy partings, as seen in
the dry and oxidised condition, but it might when water-logged
have appeared as dark-blue mud.
Since reading this paper to the Club, I have ascertained, by
the kind assistance of the rector, the Rev. J. R.Brown, that Mr.
Gibson held "Shelford Marsh" in 1725, so there can be little
doubt that the well was sunk at Great Shelford. This was
practically a separate island from Fowlness, till the tide was
more effectually shut out of the broad and easily traceable hollow
of the dividing creek.
Though no details, sufficiently complete for publication, are
obtainable of the many other wells on Fowlness, the southerly
dip in the western part is demonstrated by the successive
draining by each well of that nearest to it northwards. That at
Smallgains drained Tilebarn (on Wallasey); Little Shelford
drained Smallgains; and New House, Great Burwoods. In each
case the injured supply was restored by increasing the depth