Marvellous microfossils (Part 2): The fascination of Microfossils from the Gault of Folkestone

Joe Shimmin (UK)

The beauty and variety of the microfossils of Folkestone’s Gault Clay cliffs has amazed me ever since I was about 14 years old. At about this time, I had the good fortune to see some samples sent to me by Jim Craig, who I had met at the site. These microfossils roused in me such enduring enthusiasm that I eventually wrote an article entitled Marvellous microfossils (Part 1): Collecting Microfossils from Folkestone on how to process Gault Clay to obtain. This is the second article on this topic.

Apart from the fact that the Forams, Ostracods and other microfossils found in the residue left by wet- sieving Gault Clay are interesting and unusual, in themselves it is also a bonus that there are vastly more of these fossils, in terms of numbers, to be found than the larger fossils that people usually go there to collect. If you collected hundreds of these larger fossils from a site in one go, you might be seen to be selfishly depriving other collectors of the opportunity to collect some for themselves. However, within 1kg of Gault Clay, there are literally thousands of microfossils. Therefore, removing a few kilograms of Clay from the site will do no damage whatsoever. So, within reason, you can build up a huge collection of a vast variety of microfossils with minimal impact on the site.

These reasons have led me from writing the article referred to above to attempting to write a small book (or, rather, a pictorial guide) aimed at showing the fossil-hunting world just how good these fossils are. While writing this guide (which is, as yet, unfinished), I have learnt a number of things that I thought it would be useful to share.

The guide will show that an average collector can, with a bit of effort, survey all 11 beds in the cliffs at Folkestone’s Copt Point and, in order to write the guide, I undertook to do exactly that. The widths of the various beds at Folkestone are set out in the excellent www. gaultammonite.co.uk website and I converted these to heights above the “Sulphur band”, which is an easily identifiable layer at the very base of the Gault.

To carry out the survey, I took a surveying pole and my girlfriend, Flavia (not necessarily in that order) to Folkestone and, with her help, I was easily able to locate the heights of the different beds and extract the clay. The hard part is carrying the weight of clay taken from all 11 beds. I took about 5kg of clay from each bed, with the aim of reducing each lot to about 25g of residue. This adds up to 55kg of clay and, rather than using Flavia (for the sake of my relationship), I decided to complete the sampling across two trips – and they were both absolutely exhausting!

So, my first piece of advice is this. Unless you’re local and can make several return-trips, don’t take too much clay from each bed. 2kg from each will produce about 10g of residue that will still contain a few thousand microfossils. Also, the less clay you take, the less effort the processing takes and the less clay waste you will have to dispose of. The 55kg or so that I collected was awful to work through and it took me a month or so of breaking up the clay, drying it, soaking it and sieving it before all of my residues were ready for searching.

If you’ve gone to the effort of collecting from all of the different beds in a scientific manner, it is important that you never contaminate one sample with another. This may seem obvious. However, I have ruined several residues by absent-mindedly tipping a residue I was sorting through into the container of a residue from a different bed. This sort of thing may seem stupid, but it’s easily done. As a result of lack of vigilance, I have been forced to process yet more clay to replace the residue I have fouled.

Work on each bed in turn and store any microfossils in which you are interested in small containers, clearly marked with the bed they came from. If you are unsure of what you’ve found, it could be a number of things such as:

Forams

These are frequently spiral in shape (but not always) and are generally made up of interlinking chambers. These chambers come in a variety of shapes, such as columns, leaf- like shapes and (what I can only describe as) “angel’s wings”. The spiral ones are easy to spot but the non-spiriform ones can take a while to recognise. To further complicate things, while most are made of calcite, some are agglutinated. This means that they are made of grains of sediment “glued together”. These can look like a lump of sediment and can remain hidden to the eye until you learn to spot them. It is well worth having a look at Microfossils by H.A. Armstrong & M.D. Brasier to acquaint yourself with what you’re looking for. The variety of forms of these Gault Clay Forams makes them my favourite type of microfossil.

Ostracods (or, more usually, a single Ostracod valve)

These are easier to spot. The majority have the same basic shape of a small bean-shaped shell with varying degrees of ornamentation.

Fish and shark material

Objects that have a pleasant brown look, and are clearly not part of the sediment, tend to be parts of fish or sharks. There will be lots of small pieces that, unless you’re an expert, you won’t be able to distinguish. However, there will also be whole bones, spines, vertebrae, teeth and partial fish jaws, all of which are highly prized.

Gastropods and bivalves

These are easy enough to spot and very pretty. Watch out for the occasional tiny pearl.

Echinoderm pieces

These creatures are made up of plates. Therefore, if you find anything like that, you can safely put it in the Echinoderm category. I’ve come across pieces of brittlestar, crinoid and sea urchins (including sea urchin spines).

Fish ear otoliths

These are the ear bones of fish and are a creamy colour. They look like a flattened grain of wheat and are made of layers of calcite.

Other

There are other things to find such as small ammonites, ccaphopods, hooks (possibly from annelid worms) and more. So, keep an eye out for anything interesting.

When you have your collection and you want to mount the fossils on microfossil slides, use a PVA/water mix that is weak rather than strong. Too much glue can leave the fossil engulfed with glue residue and it’s a pain trying to get it off. Aim to glue the base of the fossil to the slide and leave everything else glue-free. This is easy enough with the larger microfossils. However, with smaller ones, it’s a battle between the glue drying out before you’ve got your microfossil onto it and having too great a blob, into which the fossil will sink and become completely covered. When you move or pick up a specimen, always use a moist brush or you’ll find that it will “ping off” somewhere and be lost.

If, for example, you want to mount a variety of Forams on a single slide, mount them one-by-one. Before gluing, avoid making the arrangement you want to achieve on a separate slide to see what it will look like. If, for the sake of aesthetics, you want to do this, make sure that you note down the position of each microfossil and its species name or, if you don’t know that, write an accurate description of it.

Also, make sure you include which bed it is from. The reason for this is that it is a virtual certainty that you will knock any arrangement of microfossils, no matter how careful you are. If it’s not glued down, the microfossils will scatter everywhere and get mixed up. If you haven’t made notes, you’ll have a load of microfossils that could be from any bed and there goes all of your hard work collecting from all of those different layers and keeping each separate for the sake of science. I have made this mistake over and over again and learned the hard way.

In these circumstances, the only advantage I have gained from my time and effort is lots of different varieties of each type of microfossil. However, I can’t say which fossil is from which bed and this is a real shame. It is said that we learn from our mistakes. However, in this respect, I hope that you can learn from mine too without you needing to make too many yourselves!

When mounted, you should have a lovely-looking microfossil slide that you will be very justified in feeling proud of. If you want to take a photo of it down the microscope, I’ve found that a regular digital camera will do a good job and the pictures seen on these pages were all taken with my Sony Cybershot W1 5.1 megapixel camera. You’ll have to play around a bit and maybe change a few settings. However, give it a go and you may be happily surprised with the results.

Finally, I can’t recommend the pursuit of Folkestone’s Gault microfossils enough. Have a go at processing some clay and I can guarantee that you’ll be thrilled with the results.

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