With good luck and perseverance, some beautiful fossils can be collected from the London Clay, which outcrops in the south east of England. The phosphatic remains of crustacea, fish and other, rarer vertebrates are well known, and information and images of them are easily accessed, particularly on the Internet site: http://www.sheppeyfossils.com. (See Fred Clouter’s article in Issue 9 of Deposits for a review of this website.) However, the formation’s hugely diverse floral assemblage is often overlooked, with little easily accessible information to be found on the web. Therefore, in this short article, I aim to introduce the most interesting of the London Clay’s plant fossils – its fossil seeds.
The London Clay Formation is a marine geological formation of Ypresian (Lower Eocene Epoch, about 56 to 49mya) age. It consists of stiff, bluish, coloured clay, which becomes brown when weathered. And it provides one of the most varied fruit and seed floras in the world, which also happens to be the only diverse flora fossil assemblage from the Lower Eocene in Europe. There are 500 or so recognised species, which would have inhabited mangrove and tropical habitats much like Indonesia or East Africa today – bordering a warm, shallow ocean. Commonly found are specimens belonging to magnolia, vines, dogwoods, palms, laurel and bay, with a third of the fossil species present belonging to genera that are still found living today.
London Clay seed fossils are preserved in pyrite. When freshly washed out of the clay, they may contain some carbon, but this is soon destroyed by abrasion or the effects of expansion and contraction due to frequent wetting and drying. The fossils are extremely varied and can represent a whole seed within a husk, a partial husk, a seed without a husk, a partial seed, a segment from a seed, a section through any of the previous and anything in between. Due to the density of the pyrite of which they are composed, seed fossils tend to be washed by the tide into accumulations of pyrite on the upper beach and foreshores of London Clay locations.
When looking for fossils, I find the foreshore to be generally more productive of quality specimens than the upper beach. Specimens are generally up to a centimetre in size and often roughly spherical. To find a good collection of seeds on a trip, you must keep your eyes very close to the ground. Knee pads are essential to avoid shredding your kneecaps on barnacle-covered rocks and they also help to keep your knees warm when kneeling on cold mud. To find larger seeds, look among accumulations of larger pieces of pyrite; for smaller seeds, hunt out finer accumulations.
When looking, keep an open mind. It is better to go home with 40 ‘possibles’, of which 20 turn out to be actual seeds, than to dismiss all but the most obvious specimens. Often, I have come home thinking that my load is probably over-optimistic, only to find that the large majority are good specimens. As mentioned, the seeds of the London Clay come in numerous shapes and forms. I hope the pictures provided in this article will give an indication of the sort of thing to look for. Key features to note are symmetry, attachment points, perfect smoothness or roundness, segments and noticeable modern seed shapes. Having said this, there are countless million, roundish pieces of pyrite on London Clay foreshores, so do bear in mind that not everything is a seed.
I’ll let the pictures do the rest of the talking. The specimens shown by no means represent all that can be found. For a better idea, I recommend the book ‘Fossil Plants of the London Clay’, written by Margaret E Collinson and available from http://www.ukge.co.uk.