SUBTERRANEAN GEOLOGY OF SOUTH-EASTERN ENGLAND. 151
while none is recorded at Meux's, Kentish Town, Crossness, Turn-
ford, and Harwich. At Loughton the boring ends at the bottom of
the Gault. In the Chatham well the thickness of the Lower Green-
sand was only 41 feet. Now Richmond is, as Mr. Whitaker remarks,
only fifteen miles north of the outcrop of the Lower Greensand in
the Weald district, at a part where it is about 400 feet thick. At
Chatham the design of the borers was to obtain a supply of water
from the Lower Greensand, which covers an unusual breadth of
country around Maidstone, eight miles due south. The uppermost
strata, the Folkestone Beds, are usually almost wholly sandy, while
the Sandgate Beds beneath them contain a considerable thick-
ness of clay; and in a well at Snodland, only five miles S.W. of
Chatham, the full thickness of these Folkestone Beds alone was
found to be 100 feet, the full thickness of the Lower Greensand at
Maidstone being estimated by Mr. Topley at 225 feet. It is thus
evident that the Lower Greensand thins away very rapidly north of
its outcrop in the Weald district, and is not likely to be found any-
where in the environs of London, unless in thin isolated patches
lying in the denuded hollows of the Palaeozoic ridge or ridges.
No Jurassic rocks are recorded as having been pierced at Crossness,
Kentish Town, Turnford, Ware, or Harwich. In the two other
borings ending in Triassic or Palaeozoic rocks the results were :—
the Oolite being directly beneath 10 feet of Lower Greensand at
Richmond, and beneath the Gault at Meux's. Like the Lower
Greensand, it would appear that Oolitic strata about London are only
likely to be met with here and there where they happen to have been
preserved in folds or hollows of the Palaeozoic ridge. Their thinning
away north of the Weald district is very remarkable. At Netherton
near Battle, the Sub-Wealden boring was made (as already stated)
during the years 1872-5. It was begun in the lowest beds which
anywhere appear at the surface of south-eastern England, the Purbecks,
the uppermost of the Oolitic series; the position of the borehole being
about 32 miles nearly due south of Chatham. The result was :—