Wednesday, 29 July 2009
Into the Devil's Hole
The Devil’s Hole (name changed) is a working quarry situated fairly close to the A1 heading north not too far from St.Neots. It is a shallow quarry in comparison with some others in the area because it is only the top 4 metres or so that are quarried.
These 4 metres of materials are sands and gravels laid down during the Pleistocene (Early Devensian) around 75,000 years ago and were subsequently scoured by glaciers during the last glacial period. Below these layers is a channel of Oxford clay dating back to the Jurassic, but this is not extracted here. Only the sand and gravel is extracted and this is why the quarry is shallow.
As you were no doubt aware, the Summer of 2007 had proven to be extraordinarily wet but in early July, after a week of rain, I arrived at the Devil’s Hole in bright breezy conditions with only occasional banks of cloud to break up the sunshine.
As the quarry is still being worked, you have to sign in and then be escorted to the area where we could start looking for fossils. The quarry itself, although shallow as mentioned, actually covers a vast area and we were taken to a couple of recently excavated areas that lie parallel to each other and these were to be our hunting grounds for the day.
Both mini-quarries were similar in layout and it was a toss of a coin to decide which one to start with. The stratigraphy of the glacial units was instantly clear as were the spoil piles of Oxford clay that were created as the excavators hit the ancient sea bed once the bulk of the sand and gravel had been extracted.
I started with the clay looking for ammonites and any possible reptile remains and after previous trips in the Oxford clay, I was expecting abundant fossils from the off. I was wrong. There was very little exposed, just the odd gryphaea and poorly preserved belemnite. I was a bit bemused by this but carried on looking convinced that there would be something, somewhere.
But still fossils were hard to come by, and after a while I decided to get up close and personal with selective spoil heaps. Since I’ve been fossil hunting, one of the best ways to start finding fossils when I’ve been struggling is to get close to the ground and start carefully sifting through dirt (or clay in this point). Today would prove to be no exception.
After a few hours of close up intense scrutinisation, I eventually found a few nice pieces including three tiny pyratised ammonites which are just a wonderful golden colour. I located one complete ammonite (species to be determined) that will need to be stabilised, a couple of beautifully preserved brachiopods, a tiny gastropod and some other ammonite pieces.
Whilst having a break and something to eat, word filtered through that some bone had been recovered from the quarry next door. “Typical” I thought, as visions of Ichthyosaur or Plesiosaur bones came to mind. For the second time I was wrong. The bones were from mammals of the Pleistocene, animals that roamed England not too long ago.
After lunch, further investigation revealed that a partial rib had been recovered, a partial ulna from possibly a bison, and amazingly enough, a mammoth task. Although, by mammoth standards, the tusk was small (about 3 feet) the tip was superbly preserved. As I was going to look in this quarry during the afternoon anyway, I hastened to get there somewhat more urgently!
This quarry was a little harder to traverse - there was water everywhere. The spoil heaps were similar though although they were very much in parallel lines, more so than the quarry next door. There was a few of us in the quarry now and I suspected that the best fossils had already been removed.
However, I was more than pleased when, after only half hour in the quarry, the chap who had found the tusk located an excellently preserved mammoth tooth only 50 yards from where I was. Today was certainly his day alright but at least it proved that were still good finds to be had.
As the afternoon wore on, nothing else was found and I resigned myself to the fact that I was probably going to end up boneless for the day. Eventually though I resorted to type and picked a likely spoil heap, got on my knees and started to look closely.
A piece of white “wood” caught my eye, roughly half-moon shape, buried in the spoil with only about 25mm exposed. Closer inspection revealed the tell-tale porous cell structure of bone and, holding my breath, I started to carefully remove the spoil around the base and the wonderful rich enamel colour of fossil bone appeared and confirmed that I had indeed found something special.
But what was it? I couldn’t determine what it was at first. It was big and held fast and I was particularly careful in removing the spoil. After 10 minutes or so I managed to remove an exquisite neck vertebra.
Unofficially it has been identified to belonging to either a bison or woolly rhinoceros – an amazing find. After carefully wrapping up the specimen, I continued to look in the immediate area for any further remains of the animal but the day was drawing to a close and, in the time remaining, I knew that further finds were unlikely.
Shortly afterward, we gathered together to compare notes and specimens. It had been a remarkable day with some nice fossils recovered. Our escort then led us from the quarries and back to the office to sign out. They had looked after us all day and a big vote of thanks is very much deserved. Thanks – you know who you are!
The rain had held off all day and I headed south for home. This was a first visit to the Devil’s Hole and I hope to return in the future, although this particular quarry is getting increasingly difficult to access, like so many these days, and opportunities are sure to be limited.
And here it is. This is an exquisitely preserved cervical vertebra from a wooly rhinoceros. Compared to some preparatory operations that are currently in progress, this was a relatively simple process. What matrix that there was was easily removed, and after a fairly standard clean up operation, the entire bone has been stabilised with B72.
The problem with sub-fossil bone of course is that I'm not absolutely certain that this consolidant will do the correct job, but it will do for now. There are those that prefer PVA for this form of bone or maybe PEG 4000. I'm hoping to get the definitive answer at SVP in Bristol during September since this form of bone preservation will be getting some deserved attention.