File:The Quarterly journal of the Geological Society of London (12684744794).jpg

276 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .May 19,
flints, with irregular seams of eocene pebbles, as shown in the an-
nexed diagram.
Section near Portobello Inn between Farningham and Wrotham.
N. Scale 12 feet to 1 inch. S.
Talus. Talus.
a. Dark ferruginous clay with flints. c. Seams of rounded Eocene pebbles.
b, b'. Light-coloured sandy loam. d. Red and yellow ochraceous sand.
e. Clay, sandy loam, and Eocene pebbles, in irregular alternations, horizontally stratified ;
becoming obscure towards the south part of the section. /. Chalk.
The materials which fill the cavities in the Portobello section, and
form the subsoil in the cuttings on the Wrotham road, have evidently
been derived from the wreck of some of the eocene tertiaries ; but, if
it should be alleged that these cavities and the deposits which they
contain belong to the eocene period, I would draw attention to the
following facts. None of the eocene strata of this neighbourhood,
which are in contact with the chalk, are of the red and yellow colours
seen in the specimens now exhibited and obtained from this section.
The lowest bed at Woolwich, Bexley, Erith, Crayford, and Dartford
is a whitish or greenish sand. Above this is a pebble-bed. The
sand generally rests on an even surface of chalk. In the few cases
in which it fills cavities in the chalk, the contents are very diiferent
from those of the Portobello section. The sands are not only green-
ish, but the flints have a dark green coating, and the lining of the
pipes, instead of being clay, is of an indurated ochreous character.
As a contrast to the contents of the Portobello cavities, I exhibit
specimens from a pipe in a chalk-pit, a little east of LulHngstone
Park. These specimens agree with the characters of the matter fill-
ing pipes in the Hampshire basin, where the chalk is there in con-
tact with the lower eocene bed. The Portobello sands and clays, on
the contrary, have more of the aspect of those which form the mid-
dle portion of the vertical strata of Alum Bay, and which Mr. Prest-
wich has identified with the Bagshot sands.
Moreover, in the immediate vicinity of Portobello there is an
eocene outlier of white sand. In a wood, marked on the Ordnance
Map as Knock Mill, but better known on the spot as Gravel-pit
Wood, there is a bed of this sand, exposed to the depth of about
12 feet. A reconstructed bed of eocene pebbles, unmixed with an-
gular and subangular flints, and imbedded in a ferruginous base of
sand and loam, abuts abruptly against the western edge of the sand,
as far as can be judged from the obscure state of the section disturbed
by the operations of digging gravel. The contact of the sand with
the chalk is not exposed ; but the rock must be very near the bottom