Project 7: Fossil Shells


Does it strike you as odd that whilst walking to work at the University along a ridge some 70 metres above sea level and some 150 km from the sea that I repeatedly find shells? It struck me as odd! Surely one of us is in the wrong place and I am not standing underwater where once these shells lived? Mysterious!

The objective of this speaking project is to use research to reinforce a talk. Where better place to start than with a mystery. Toastmaster, fellow Toastmasters and most welcome guests I set myself the challenge of learning the story of the shells coming to be in the soils along my walking route and in so doing enrich my appreciation of the world around.

In the beginning

So what are these shells? On family visits to the Bedford Museum and the Harold Odell Country park to the north of Bedford I became aware that fossils exist in the area and that there is a Bedfordshire Geological Society. Bedfordshire Geology Society leaflets show the fossils to be Gryphaea –the Jurassic oyster. They are bivalve molluscs that would have lived on a sea bottom as filter feeders. The stronger left half shell is often found, but rarely the thinner right half.

My next line of enquiry took me to Tim Farewell, a colleague here at the University. The University is the home of the national soil survey in England and it forms part of a number of spatial Geographical Information Systems about land. These are LANDIS reports from points along my walk. He has worked with the local Geological Society to integrate data on soils and land with the data on geology. They have published this paper in a learned journal

Time line

The Jurassic Oysters are found in the widespread 150m year old Jurassic clays that make up the solid geology of North Bedfordshire. Clays are formed by the sedimentation of the finest particles carried off land and into water by the process es of erosion. These jars contains different soils in water and if you shake them you will observe them slowly settling out with the heaviest particles first. The processes of land erosion are continuous.

200m years ago the supercontinent of Pangaea is breaking up as the Atlantic forms due to tectonic activity and the seas are breaking in. 190m years ago in the early Jurassic we have sedimentary rocks like sandstones and limestone. Around 150 m years ago the seas became deeper and land further away and clays. 100m years our Gryphaea has been covered in green sand and Gault clay in the early Cretaceous.  65 m years ago we have seen chalk formed. Europe is 100 m (the length of a football pitch)under a tropical sea and chalks form from the skeletons of Nanoplankton in pure clean water. There is nowhere left on Earth where chalks form today. I was surprised to discover that flints form in chalk in the cavities created by sea life and might be form from the gelatinous remains of sponges that get trapped in the rock.

2 millions years ago the Alps and Chilterns are pushed up as the African plate comes North. Half a million years ago where we stand is under 40 m ice sheet and we are on a 70 m layer of glacial grinding paste which is the upper geology of this area. Only the high chalks above Luton survive intact from the upper Cretaceous. The glaciers recede dumping their grinding paste as glacial till that is what we see as soil –calcareous brown earths. The flints, fossils and some limestone are tough enough to survive and remain in the till.

The wider picture

The common name for Gryphaea is Devil’s toe nails. One can see why! I Googled for more information concerning the Folklore of these fossils. That led me to the Natural History Museum and the department of natural history at Birmingham University. In the 17th and 18th ground Gryphea was taken as a folklore medicine for hard knobbly rigid painful backs in horses and man. It is an example of a Sympathetic Medicine. We relate how we feel to something else and assume that it must be good for us. Other examples found on the internet include Rhino horn and male tiger gentalia for virility.

The Jurassic clays are the foundation of Bedfordshire’s, once vast, brick industry. The clays in Bedfordshire contain carbon which combusts to assist with firing, saving 20% of the energy costs. Tim told me It was a full time job to pick fossils out of the raw clay at the brickworks.

Being sedimentary the solid geology around here is flat with up to 70 m of glacial till dumped on. top That leaves a landscape of plateaus cut through by drainage by rivers. Those plateaus proved an excellent location for WW2 airfields of which there are many in North Bedfordshire and of which the University is one.


There are four main messages that I take away.

Firstly, over time global change processes are huge and perhaps NOW I will be much more mindful of the impact that man might have on them via climate change;

Secondly, flints maybe crystalline but they are not volcanic but perhaps form in chalk cavities by silication of gelatinous materials under pressure and heat. They can contain fossils;

Thirdly, the concept of sympathetic medicine in folklore reminded me NOT to underestimate the mind in the way we perceive ourselves and the world around. Placebos can have a life of their own;; AND

Finally, the geology and natural resources of an area explain a lot of the form and cultural history of the landcape.

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