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Small and perfectly formed

Beaminster’s Horn Park is the country’s smallest National Nature Reserve, yet still one of the richest in fossils, as Joël Lacey discovers

After the back face of the quarry was cleared of grass and cleaned

After the back face of the quarry was cleared of grass and cleaned

According to Brian Earl, the Curator of Beaminster Museum: ‘It is probably no exaggeration to claim that more Beaminster residents associate Horn Park Quarry with somewhere you can buy a new bathroom than with a nationally important fossil bed. In all likelihood very few shoppers will even have noticed the gates of the National Nature Reserve at the far end of the small industrial estate, and some of them may not even be aware of its existence,’ Brian adds.
The gates of the county’s smallest National Nature Reserve may not be intimately familiar to all those visiting it, but its size, location and near neighbours are in no way an indication that there is anything less than spectacular about the Horn Park Quarry reserve.  Sam Scriven, Jurassic Coast Earth Science Manager, explains the background to why Horn Park Quarry is so important. ‘The inferior oolite [the yellow sedimentary limestone in the quarry] formed in a shallow tropical sea around 170 million years ago. One of the things people find hard about looking at a vertical cliff face is understanding that there was geography happening to that area as layers were being laid down just as there is now (so there were cliffs and forests and bays etc) and that all sedimentary rocks are the result of different processes at different times. We know that the inferior oolite records, in total, around six million years of the Jurassic period, but that is pieced together from different exposures, like a jigsaw puzzle. At Horn Park Quarry, there is probably about 5m of rock exposed, and the bottom half of that covers roughly the same amount of time as is represented in a layer of 1cm thick in the cliff at Burton Bradstock. Horn Park Quarry is one of the most complete records of inferior oolite anywhere. It’s the closest thing we have to a picture on the top of the inferior oolite jigsaw box’
How do we know this? Sam explains further: ‘The way we work out geological ages is by fossils; If you imagine that the rock layers are the pages of a book then the ammonites are like the changing page numbers because they have evolved through time, so by looking at different sites you can see the ammonites in a particular order. If you see ammonite A and ammonite B together, but at another site, you see A, B, C and D, you know there a longer period is covered in the fossil record. At Horn Park Quarry two periods – Aalenian (170.3–174.1 million years ago) and the Bajocian (168.3–170.3 million years ago) – are strongly represented, and Horn Park Quarry has the most complete record of Aalenian ammonites anywhere in the country.’

Inside an ammonite found at Horn Park Quarry

Inside an ammonite found at Horn Park Quarry

The scale of the fossil record in that narrow middle Jurassic period, is also useful for matching sites of a similar age around the world. ‘It helps us,’ Sam says simply, ‘understand earth history’.
‘Other things that are important is that it’s a really well preserved quarry site, many quarries have been ‘restored’ ie filled back in. And on the coast or in railway cuttings there is always a risk in trying to access the exposures. There’s a particular feature that is exposed at Horn Park Quarry that isn’t exposed anywhere else,’ says Sam. ‘Every so often, a storm could come through and rather than rock being laid down it is eroded. So layers that were solidifying or hardening get wiped away. These bits are great for quarrymen as what they did was to use one of these bedding planes to lift the usable stone off it and it also shows some of the half formed fossils that have been sliced through. When you are walking across that layer you see these exposed interiors of fossils.’
Obviously not everyone is allowed to do just that, though, as access to Horn Park Quarry is restricted owing to a period of what is referred to as ‘irresponsible fossil collecting’ – ie destructive wholesale taking of fossils. If left unchecked, this would result in the degradation of this sensitive site.

Yet more ammonites

Yet more ammonites

Do not despair if you are not a geologist, though, there are other means of viewing the site’s treasures.
‘Beaminster Museum is delighted to have such a fine piece of the Jurassic Coast on its otherwise inland doorstep,’ says, Brian Earl, adding ‘despite frequently having to point out to disappointed visitors that it does not in fact own Horn Park Quarry and cannot let people in at the drop of a hat.
‘One of the museum’s fundamental aims is to make local history as accessible as possible to as wide an audience as possible. It relishes the opportunity to try and describe the wonders of Horn Park Quarry remotely. Thanks to the Curry Fund and the invaluable help of experts like Sam the museum gallery houses an impressive display of wall-mounted fossils and offers a tantalising glimpse into a warm shallow sea full of ammonites, complete with heads, legs and all the other bits that failed to withstand the ravages of time. It also tells the story of Horn Park Quarry set against the basic background of changing sea levels and deposition.
‘No attempt has been made to dumb geology down,’ Brian explains. ‘The aim is to demystify it wherever possible. Terms like ‘”inferior oolite” are explained in plain English. Visitors of all ages tend to linger by the exhibit. There are activities for the younger generation ranging from scrabbling in a sandbox for smaller fossils to completing an ammonite puzzle using the Fibonacci Sequence.
‘The museum hosts regular school visits and the display is a natural draw, even when focus is supposed to be elsewhere! Some visits can be combined with a special trip to the quarry. Once the children realise the museum has nothing earth-shattering to offer on the dinosaur front, fossils are definitely the next best thing. Groups of geology students from Truro College also make the museum and quarry must-see elements of their annual field trip to Dorset. Visits to the quarry by small groups of adults can also be arranged through museum volunteers.’
In other words, Beaminster Museum might be seen as the informational (and perhaps equally important, indoor) arm of Horn Park Quarry, and a useful means whereby the understandably secret world of the quarry can reach a wider audience. The combination of the Horn Park exhibit and the availability of loans boxes filled with fossils for schools in Dorset and beyond means that the museum continues to play its part in spreading the news to all parties, not least the next generation of geologists.

Beaminster Museum's ammonite box, which is available for loan to schools

Beaminster Museum’s ammonite box, which is available for loan to schools

Back at the quarry itself, Sam Scriven is now into his seventh year of association with the project: ‘In 2009 I was given the job of helping Natural England preserve the site and to gain access to the fossils there. We actually swept that off to get rid of weathered rock and then washed it off, we cleared off all the plants and cleared off the vegetation and soil that had built up from the vertical faces.
‘That work took place over about three years, to bring the site up to a decent condition and all that work culminated in creating a new exposure, and it’s important for managing this site to make sure the new exposures were in top condition.
‘We wanted to create a small area of 4 metres by 2 metres down through five layers to show people the amazing fossils. What we also did was to bolt in a lockable coverable frame to protect it from the weather and also to keep it safe.

An exposure, the coverable and lockable section of fossil-rich rock

An exposure, the coverable and lockable section of fossil-rich rock

‘The fossils can pop-out, but they are in-situ fossils and that’s the exciting thing and you see how they change through time. Through that process, lifting off these layers of rocks, there were fossils coming off that as well; we managed to collect 30 ammonites of museum quality and schools can borrow a box of these. What we would like to do, Sam says, ‘is to do a second, dig; to expose layers lower than those we dug previously. The way the set-up works is that Natural England are in charge of the site, I am the expert adviser and the Museum facilitates access in terms of physical access (visits) and virtual access (via the exhibition in the museum). For the new exposure, we would follow the same principles as before and Bob Chandler (the inferior oolite expert) would be on hand to plan the excavation and then we would probably get in two expert excavators who are vastly experienced in digging. It would have to be funded and managed by Natural England, who run the site, and that funding is not yet in place.’

Not your average, everyday, ho-hum, run-of-the-mill National Nature Reserve

Not your average, everyday, ho-hum, run-of-the-mill National Nature Reserve

Whatever is yet to come out of Horn Park Quarry in the future, though, it is already astonishing to think that an area smaller than a supermarket car park, by the side of an industrial estate in Beaminster is the Rosetta Stone of the middle Jurassic period.
❱ http://jurassiccoast.org/fossilfinder

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