Joe Shimmin (UK)
The Gault Clay outcrop, at Folkestone in Kent, is a wonderful place to ﬁnd all manner of fossils. Over 100 species of ammonite have been found and there are also barnacles, belemnites, bones (reptile and ﬁsh), coprolites, corals, crinoid pieces, crabs, crocodile teeth, ﬁsh teeth, gastropods, (deep breath) nautiluses, ccaphopods, shark teeth, vertebrae (bony ﬁsh, shark and, occasionally, reptile), worm tubes and more. These fossils can be found in the clay cliffs and also at the base of the cliffs, washed out from above. But there are other fossils to be found at Folkestone that are less conspicuous.
An individual, who is new to the site, may be forgiven for thinking that the larger fossils are all that Folkestone has to offer. If this were so, it would still be a fantastic location. The fact is, however, that this is not the case. Folkestone’s Gault Clay also has a rich and varied, beautifully preserved, microfossil fauna.
Microfossils are trickier to ﬁnd and collect than their larger counterparts. They are hard to see, often quite fragile and difﬁcult to handle. However, with a small amount of perseverance, along with a good technique and a few pieces of apparatus, anyone will be able ﬁnd hundreds of these beautiful and intricate fossils and, in no time, build up quite a collection. While on a fossil hunting trip to Folkestone, it is well worth thinking of the Gault’s microfossils and the following is a full method of how to ﬁnd, extract and exhibit them.
First of all, you will need to collect some clay. The Gault Clay at Folkestone is many metres thick and its various beds yield different numbers and varieties of fossils. If you don’t live nearby, and you’re only visiting for a little while, I’d advise taking clay samples from various heights (and therefore beds), as the microfossil assemblage will be different for each. It is best to know which beds you have taken your clay samples from, as this will be useful when you come to identify your fossils. If this is too complicated for you – and it often is for me – then take notes on the height above the beach that the clay sample comes from, as well as the characteristics of the surrounding clay (that is, its colour, texture, whether it is mottled or not, and the identity of any fossils you ﬁnd in situ).
The layers of clay, which yield the most microfossils, are also the layers that contain plenty of fossils. Some areas are packed with shell debris and I usually collect from these – with good results. Take about a third of a carrier bag full of clay from each part of the cliff you want to sample, obviously only collecting from places that you are conﬁdent are safe. This is the only ﬁeldwork required for collecting Folkestone’s microfossils. For the rest of the time you are there, you can look around for some or all of the fossil types listed above.
When you have got your clay samples home, you’ll need to break the clay down to release the fossil specimens from their surrounding matrix. To do this, break up the lumps of clay into pieces, one inch cubed or less, and then dry them out thoroughly in an airing cupboard or an oven on a low heat. If it’s a sunny day, you could leave them outside until you are conﬁdent that they are fully dry. When dried, ﬁll up a bucket with hot soapy water and transfer the clay into it. You’ll obviously need to process each of your samples of clay separately so as not to contaminate one sample with another. Leave the clay to soak for a day or so and, in this time, it should break down into a sludge, releasing the fossils that it contains.
To recover your microfossils, you will need two sieves, one for the larger specimens and one for the smaller ones. I use Endicott sieves of mesh size 1mm and 300 microns available from UKGE. However, for a ﬁrst attempt, you could try a regular household sieve for your large mesh size and muslin stretched across a piece of drainpipe for your small mesh size. Take some of your sludge and, with plenty of water, wash it through the sieves (one on top of the other). The very ﬁne clay particles will be washed through, leaving behind the larger cost money. Dry your microfossil residue out and, when it’s dry, give it another wash through the sieves – this will get rid of any remaining clay particles. Transfer the residue into a beaker of water and ﬂoat off any modern day vegetable matter such as the little roots that are often found in the clay cliffs. Lastly, dry out your residue and then you’re ready to hunt for microfossils.
To ﬁnd the microfossils, pour out a thin layer of residue onto a ﬂat-bottomed dish with a 1cm grid drawn onto it. You’ll need a low power binocular microscope (10X magniﬁcation upwards) or a decent magnifying glass to spot the fossils. Work your way across the dish, moving onto the next square of the grid when you have completed the one before. When a microfossil is found, pick it up with a ﬁne paintbrush moistened with a little water, and transfer it to a small sample tube. Keep going until you have looked over objects that the clay contained. (I mean “larger” in comparison to the clay particles.) This is your “microfossil residue”.
Amongst this residue will be plenty of pieces of original ammonite shell as well as foraminifera (tiny single celled animals with a shell superﬁcially resembling an ammonite’s), ostracod valves (the shells of minute crustaceans, otherwise known as seed shrimps), and small gastropods. Also present will be occasional shark teeth and ﬁsh parts, tiny crinoid ossicles and other small fossils. I’ve even found a little fossil pearl before.
Avoid washing the clay sludge down the drain – it’ll block it. It’s much better to do this type of work in the garden as blocked drains the whole of the residue in the dish and, by that time, you should have picked up numerous, tiny, beautiful fossils.
These fossils can be mounted onto a palaeontological slide, available from UKGE, using PVA glue mixed in equal parts with water. The glue dries clear and does not obscure your specimens. With a little effort, you will be able to build up an extensive collection out of just one sample of clay. If you’ve not found these types of fossils before then welcome to the wonderful world of microfossils.
The second of my articles on Gault microfossils from Folkestone is Marvellous microfossils (Part 2): The fascination of Microfossils from the Gault of Folkestone.
Thanks to the late Jim Craig who introduced me to Folkestone’s microfossils about ten years ago and to Fossils of the Gault Clay & Folkestone Beds of Kent for microfossil identifications.
Image of Folkestone cliffs by Joe Shimmin. Macro images by Stuart Handley.
Reference and further reading
“Marvelous Microfossils: Creators, Timekeepers, Architects“, by Patrick De Wever, foreword by Hubert Reeves, translated by Alison Duncan, The John Hopkins University Press, Baltimore, Maryland, USA (2020), illustrated edition, 255 pages (hardback), ISBN-13: 978-1421436739
“Microfossils” (2nd edition), by Howard A Armstrong and Martin D Brasier, Wiley-Blackwell (2005), 306 pages (softback), ISBN: 978-06320527-9-0