150 SUBTERRANEAN GEOLOGY OF SOUTH-EASTERN ENGLAND.
Dockyard Extension) 682 feet6 The extra thickness at Harwich is
what might be expected when we remember that further away in the
same direction, at Norwich, the thickness of the Chalk was found to
be 1,146 feet. (Wh.)
The Upper Greensand is a very thin and unimportant bed in the
eastern part of the Weald district, though it thickens westward so as
to make a fairly conspicuous escarpment on the Hampshire margin,
and is prominent as the crag bounding the Undercliff of the southern
shore of the Isle of Wight. It is recorded as being 77 feet at Ware,
and 12 feet (Wh.) or 65 feet (Wo.) at Crossness, its thickness at
Turnford being 31 feet, at Meux's Brewery, 28 feet, at Richmond,
16 feet, and at Kentish Town, 13 feet. None was recognized at
Harwich, and 30 feet at Loughton, This bed often resembles the
Chalk so much that it is sometimes a matter of some difficulty to say
exactly where the dividing line should be drawn. Doubtless its thick-
ness would have been found to vary very much less had its boundary
been determined in each case by the same persons. Mr. Whitaker
thinks the Upper Greensand at Ware was probably nearly all Chalk
marl, and that at Harwich some may have been included in the Gault.
Below the Upper Greensand the Gault clay was found in every
case. Its thicknesses were :—
Thus the thickness of the Gault in the neighbourhood of London
was found to vary as little as that of the Chalk. But to the north-
east the Gault, instead of thickening like the Chalk, appears to become
thinner, being but 61 feet at Harwich, and at Holkbam, near Wells,
Norfolk, only 10 feet. Hitherto in our downward progress we have
met with nothing in the least degree abnormal, but from the bottom
of the Gault we find an almost entire absence of Lower Cretaceous
and Jurassic rocks in the borings ending in Palaeozoic or Triassic beds
The thicknesses of Lower Greensand were :—
6 See W. Whitaker, "On some borings in Kent," Q. J. Geol, Soc, vol. xlii., 1886. A section
added to this paper by Mr. Whitaker, across the Weald of Sussex and Kent into Essex, admirably
illustrates the thinning of the Jurassic rocks northwards.