By Phil Eyden
Note: Phil welcomes discussion on this article in the Fossils and History forum on the Message Board.
Folkestone is located at the extreme
southeast tip of
The earliest rocks at Folkestone consist of
Lower Greensand exposed to the north of the town and run through a sequence of
Lower Greensand, Gault Clay (phasing into Upper
Greensand) and Chalk, the whole sequence dating from approximately 120 to 80
million years old. The chalk increases in thickness to the north culminating
with the famous white cliffs of
It is the Gault
Clay that is of particular interest; it is a dark blue-grey colour and has been
extensively studied. The clay consists of mudstones with layers of phosphate
nodules that delineate the margins of some of the clay beds,
the whole Gault sequence achieves a thickness of 40m
in places. The clay has been sub-divided into thirteen individual beds, each
containing diagnostic fossil species and dates from the Middle to the Late Albian of the Cretaceous period, approximately 108-97.5mya. The clay from
the Middle Albian is known as the
During the Albian
period of the Cretaceous much of what is now southern
The Gault contains the fossils of many forms of marine creature; ammonites, belemnites, nautilus, bivalves, crinoids, gastropods, fish remains, and scaphopods are quite common along with rare finds of reptilia. Ichthyosaur vertebrae have been found in association with the smaller fauna though by far the most common fossils are the small shelly forms. In some of the clay bed sequences the fossils are preserved in phosphate; they tend to be dark, frequently broken and are often in concreted masses. The best preserved fossils are those that are pyritised, the preservation of these pyritised animal remains in the some of the Lower Gault beds is exceptional, shells tend to be preserved in their original proportions and are generally not crushed. Sometimes a beautiful coating of iridescent mother-of-pearl is to be found though this is usually partial or flaked off entirely. They do require careful preservation (more on that subject later).
The ammonite fauna is quite diverse with
many different species present. During the later part of the Lower Cretaceous
the ammonites suddenly radiated with a rapid burst of evolutionary activity,
the most common group of ammonites found at Folkestone were part of this phase.
Many of the local ammonites belonged to the Hoplitaceae,
a European ammonite super-family that that is characterised by its highly
ornamented, generally spiky form, small size and tubercles. The Hoplitaceae, a long lived and true ammonite family, thrived
from the Early Albian but went into decline towards
the Late Cretaceous becoming extinct at a date of roughly 83 million years ago. The extent of the domain of
this super-family stretched across European waters from the recently separated
North America (members of this ammonite group have been found in Florida) to at
least as far as Iran and central Asia, and is known as the 'Hoplitinid
Province' by palaeontologists. The specific species of the Hopitidae
that one finds at Folkestone tend to be confined to the Gault
There are a number of variations within the Hoplitidae that can be found at Folkestone, with genera of the strongly ribbed Hoplites, the smoother more delicate looking Anahoplites and the robust, ribbed and spine-bearing Euhoplites being the most common. Other members of the group that can be found include Dimorphoplites, Epihoplites and Otohoplites. None of the species belonging to these groups were very long lived, it is estimated that many of these ammonite forms lived only a few hundred thousand years, hence they can be used as a useful tool in stratigraphy in attempting to determine layers; various beds in the Gault clay each has its own 'marker' species.
Not all the ammonites are from this family.
There is a wide range of other ammonites, notably the strongly ribbed Hysteroceras, a member of the Acanthocerataceae. Also from this family, the
and Dipoloceras with heavy keels on their shells are not
uncommon, though usually fragmentary. Increasingly common in the
Belemnites are extremely common; one would be unlucky indeed not to find one within five minutes of studying the clay outcrop. These belemnites are normally 2-4cm in length and are one of the smallest genus, Neohibolites. Marked variations in the shape of the tip of the rostrum makes identification of individual species possible. These belemnites are extremely resistant and wash out of the cliffs to become a common find in the shingle amongst the boulders on the beach. The calcite belemnite rostra have a translucent quality and sometimes traces of the internal structure and phragmocone can be determined. Neohibolites had a worldwide distribution and probably lived in vast shoals on the warm continental shelves from a date of about 112 million tears ago in early Albian through to the succeeding Cenomanian period of the Cretaceous, probably becoming extinct about 93.5 million years ago.
Nautilus specimens are rarely found and are
much more uncommon than ammonites, nonetheless at least one genus is known, Eutrephoceras clementinum.
Interestingly, unlike the ammonites, this nautilus had a worldwide distribution
and other examples of species of this nautilus are known from areas as
geographically separated as
Ammonites are by no means the only fossils
that can be found. Although one would be fortunate indeed to find an
ichthyosaur vertebra these are not unknown as are occasional rare finds of
turtle remains and plesiosaur bones. The majority of the fossils are of small
marine invertebrates; aside from
Many of the fossils are preserved in black phosphate, these merely require cleaning and no further treatment. Some of the Gault layers contain fossils, frequently crustaceans, in small brown pebble sized nodules. These can be cracked open with caution with a hammer but one must be prepared to lose the odd specimen. Frequently these nodules are harder than the fossil inside, so shattering is common.
As mentioned above, the best fossils including many ammonites are those that are preserved in iron pyrites. These can cause problems as if left untreated as they will disintegrate over a year or two as iron pyrites is inherently instable when exposed to air. Prolonged exposure to oxygen without some form of protection from lacquer or varnish will lead to a creeping decay and slow disintegration. One can't just wash them and leave them, unfortunately. Fossils are best left to soak for a week or so in fresh water which should be enough time to remove the salts that also accelerate decay. One can usually tell when this is happening, as tiny bubbles tend to form on the surface of the fossils, after a few days this ceases. Then leave them to dry, and should be treated with lacquer, a mixture of PVA and water, or can be varnished with modelling varnish. If you use this approach, satin varnish gives a nicer effect than gloss. The fossils can then be mounted in display boxes, with a label. This keeps the fossil in a sealed environment and prevents it from being knocked about and damaged. Boxes are available from many mineralogy suppliers; if ordering from within the United Kingdom UKGE Ltd is a good source of inexpensive display cases.
If anyone is thinking of going to site
please be aware that the site is poorly accessible. Although parking is very
easy along the side roads overlooking
Fossils are best collected from the beach as opposed to the cliff itself as wave and rain action tends to wash specimens into the shingle in between the boulders on the beach. Turning over stones and careful scrutiny of the clay outwash amongst the shingle usually produces the best results. One really does not require a hammer or pick, a trowel will suffice to sort through the stones and sediment. A bottle of tap water is also advisable to wash finds on the spot if one is curious and wishes to wash the clay off there and then. One is advised to take a bag and newspaper to keep the specimens safe and free from knocking into each other.
Above all, be careful, but have fun. Just ensure you post images of what you find here first!
Fossils of the Gault Clay and Folkestone Beds,
Very detailed look at Folkestone fossils and the stratigraphy of the area including many stunning images. Very useful for finds identification.
Adders.org: Folkestone Fossils.
A nice short guide to Folkestone Fossils for kids:
UK Fossils guide to Folkestone.
Plenty of excellent images of location and site available here:
Geology of Kent and the Boulonnais.
Detailed look at the geology of
Les Ammonites du Cretace
More fantastic photographs of Lower Cretaceous Albian ammonites are available on this French site:
Excellent site for
information on all aspects of fossil hunting in the
PaleoGlobe adapted from Dr Ron Blakely's Home Page: http://jan.ucc.nau.edu/~rcb7/RCB.html
Thanks to Mandy Whall for the loan of the Anahoplites planus specimen.
Thanks to the barking mad Daisy the Dog for providing scale in the stratigraphy photograph and providing on-site entertainment by straddling a rock and struggling vainly whilst unable to free herself.