TRANSACTIONS
OF THE
HULL
GEOLOG ICAL
SOCIETY
ABSTRACTS OF LECTURES.
February 19th,
1895.
FOSSIL ZONES OF THE LOWER CHALK OF THE
Rev. H. E. MADDOCK, M.A.,F.G.S.
Mr. Maddock said the sections of the chalk in the South of England were much
more easy to work out than they are in most parts of the North of England.
He had worked continuously for three years at the lower beds of the Upper
Cretaceous series which were then, magnificently displayed between
Eastbourne and
The lecturer then described, in ascending order, the position and character
of the successive beds between the Wish-point near Eastbourne and Beach),
Head which rises to the height of 600 feet, three miles to the West.
THE GAULT.
Eight feet of the upper part of this bed,
almost entirely
unfossiliferous, forms the base of the cliff at the Eastern corner of the
Wish- point.
THE UPPER GREENSAND
Forms the upper and remaining part of the cliff at the Wish-point. In the
lower twenty-six feet of this bed fossils are rare, but immediately above,
occurs a hard bed (4 feet) often called the Chloritic Marl, (corresponding
to the well-known Coprolite Bed at Cambridge) crowded with fossils, mostly
in the form of phosphatic casts.
CHALK
Is thirty feet thick and forms the base of the cliff for a quarter of a
mile. At its base occurs the Sponge bed one foot in thickness, full of
branching sponges formerly called
Brachiolites, now called
Plocoscyphia moeandrina. This bed may be regarded as a transition bed
between the Chloritic Marl and the Chalk Marl. The Chalk Marl consists of
hard bands of bluish white argillaceous chalk, about one foot thick in which
the chalk seems to be almost conchoidal in structure. The Chalk Marl is
fairly fossiliferous, and may be put down to the Zone of Ammonites Varians
and Rhotomagensis -- Rhynchonellae are very abundant. The chief echinoderm
is Holaster levis var.
Trecensis.
CAST BED.
Six feet thick and called locally the Scaphites bed. May be regarded as a
passage bed between the Chalk Marl and the Grey Chalk. It is more thickly
bedded and softer than the chalk underlying it and abounds in fossils,
chiefly in the form of casts. From this stratum, not far from the
GREY CHALK.
Eighty feet thick, consists of thick beds of hard Grey Chalk separated by
marly bands of a few inches in thickness. It forms the base of the cliff
till nearly the middle of
BLUE BAND.
Ten feet in thickness, forms the base of the Synclinal at Holywell Bay,
where it occurs in the form of two bands of argillaceous chalk, very hard
and compact, separated by a whiter chalk band of three or four feet. The one
fossil, fragments of which are plentiful, is
Belemnitella plena, which gives
its name to the zone.
The bed may be regarded as a transition bed between the Middle and Grey
Chalk, belonging rather to the lower beds than the upper.
GRIT BED.
Thirty feet thick. This bed begins the Middle Chalk and consists of thick
courses of extremely hard crystalline chalk, almost entirely made up of
fragments of shells chiefly
Inoceramus Mytiloides with numerous specimens of
Terebratulina gracilis and of a
small Echinoderm, Discoidea minima.
Between these thick beds are bands of nodular chalk, described as brecciated
and concretionary, Homomomy, formed apparently of rolled fragments of
locally called the underlying beds in a matrix of exceedingly hard siliceous
chalk. This proves clearly that there is here a definite break in the
Cretaceous series, and it is about this horizon that M. Barrois separates
between the Cenomanian and the Turonian series.
Above the Grit beds before the first flint band is reached, comes one
hundred and twenty feet more of massive chalk in thick beds, the
characteristic fossils of which are
Echinoconus subrotundus,
Rhynconella cuvieri and Spondylus
spinosus. About twenty feet below the flint band the bed changes in
character both lithologically and paleontologically. The chalk becomes
whiter and softer and is filled with
Ventriculites in the form of casts,
Ventric. impressus being
especially plentiful while the characteristic
Inoceramus is
Ioceramus brongniarti and
Micraster cor. bovis is
occasionally found. It is interesting to notice the great difference in the
thickness of the chalk between the blue band and the lowest line of flint in
the different parts of
At
At
At Hitchin the
thickness is about 45 feet,
At
At Speeton the
thickness is about 8 feet,
Mr. Wm. Hill in the Quarterly Journal of the Geological Society of
In conclusion Mr. Maddock said that the notes from which this lecture had
been compiled were made before M. Barrois's visit to
Copyright Hull Geological Society 2016