xiv Journal of Proceedings.
where the Thanet sand had been breached, and was the subject of an
exposition from Professor Morris. Its surface showed the mammillated
appearance so frequently found in these concretions. (Some very large
and characteristic examples are to be seen in the adjacent village, near the
wharf of the Grays Chalk Quarries Company.) The Professor pointed
out that these rounded appearances were not due to the wear and tear of
transport. A thin flake examined by the microscope would show the
sandstone to be composed of subangular quartz grains, and not of these
grains rounded. Looking at the range of the Bagshot and Thanet sands,
which at one time extended all over the valley of the Thames, he was
inclined to consider these Greywethers as derived from the indurated base
of the latter ; the softer sand had been carried away by denudation.
On reaching the floor of the pit, which is excavated one hundred feet
into the chalk, the party examined the fine vertical sections which are
there exposed, consisting of upper chalk, with green-flint bed, Thanet
sand (in some places twenty-five feet in thickness), and High Terrace
Thames Valley drift. Some of the "sand-pipes" here are sixty and
seventy feet in depth, partially filled, in some, instances, with gravel, and
in otheis with Thanet sand. Sir Antonio Brady, who was present, called
attention to one of the more remarkable, which had penetrated below a
horizontal band of flint without disturbing it. Mr. Walker gave a
general account of the structure and composition of the rocks here
exposed; the chalk, with its marine organic remains, more especially its
sponges, corals, "sea-urchins," mollusca and fishes (a large number of the
curious palatal teeth of Ptychodus and other sharks were shown sub-
sequently) ; the Thanet sand, marine but unfossiliferous, near London ;
and the "High Terrace Thames Drift" of Professor Prestwich and Mr.
Whitaker (the "Marine Gravel" of Mr. Searles Wood). Prof. Morris
followed with a comprehensive review of the history and former range of
the chalk, Thanet sand, and other Eocene beds now missing below the
gravel, especially descanting upon the great physical changes which had
taken place in the face of Europe (such as the elevation of the Alps), in
the interval denoted by the absence of the Woolwich beds, Oldhaven
pebbles, London clay, and Bagshot sand. Referring to the Green-flint
bed (the "Bull-head bed" of the workmen), Professor Morris called atten-
tion to the well-marked concentric structure of many of the flints,
probably owing to the presence of iron, which tends to this arrangement.
The solvent action of carbonated waters, which formed the "pipes," was
also seen, the Professor said, in the undulating surface of the chalk, as
traced by the course of the green-flints. The depressions in this line
were therefore posterior to the elevation and desiccation of the sea-bed.
With regard to the absence of Woolwich beds and London tertiaries which
once overlay the Thanet sands, he pointed out that the Woolwich beds
were found about a mile further inland, at the village of Stifford, and he
would suggest to the Essex Field Club an examination of them at that
spot, inasmuch as the only instance of a certain shell of the Woolwich