Fossil Hunting on the Isle of Portland on the Jurassic Coast of Dorset - Pt 1

Fossil Coast Drinks Co is pleased to introduce Steve Snowball as a guest blogger who will be sharing his knowledge, experience and expertise about fossil hunting on the Isle of Portland along the Jurassic Coast near Weymouth in Dorset. Steve is an accomplished author of "A Guide to Fossil Collecting in England & Wales" and co-author of four other highly acclaimed guides to fossil collecting on the Dorset coast.

Despite the somewhat bleak environment and often hazardous conditions, with sheer drops into the wild sea beneath, the Isle of Portland is able to deliver an interesting experience for the fossil collector.

There are certainly a few places which provide safe opportunities for collection and importantly, avoiding any treacherous terrain. Of course, fossil collecting along the coast will always have some element of risk, whether from the tides, the cliff rock falls or inclement weather.

The Isle of Portland is no different and the advice is to always let someone know where you are going and what time you might be expected back. In hot weather, be prepared to take plenty of water and sun creams and in cold, wet conditions to wear sensible clothing and footwear. Slippery rocks can cause unwanted injury! Importantly, always check tide times when collecting from any coastal location.

The Isle of Portland is well known for the hard Portland Stone, which has been used for centuries for building material. Much of London’s historic architecture was built of this material and includes St. Paul’s Cathedral, the British Museum, parts of Buckingham Palace, the Tower of London and many others.

The island is scarred from the intense quarrying that has taken place wherever the years. The stone in this small concentration of land has distinct and various layers, creating a collection of closely related textures – each with its own distinct character and qualities, depending on its age.

The old quarries, such as the one shown above, can provide interesting fossil hunting and many are open to the public as nature trails or for walking/ leisure areas. Searching the old spoil tips and loose rocks can often reveal fossils, most usually of marine life, especially bivalves.

The three main variants of Portland Stone are:

These layers make up the sloping plateau of Portland, which falls 152 metres in the north of the island, too just over 6 metres at Portland Bill in the south. The weather resistant rock is underlain by Portland Sand, which rests on the Kimmeridge Clay Formation. This fossiliferous clay is clearly seen outcropping at the base of the cliffs at West Weare, in the north-west of the island.

The cliff section at West Weares is easily accessed from the end of Chesil Beach at Chiswell. Car parking is easy and then you can follow the coastal path, which follows the new sea wall. This locality provides some of the best collecting on the island. You will need to be careful and agile in order to scrambler up the lower but less steep, flanks of the Weare, where quarry overburden was tipped in days gone by. The previous sheep grazing area is now full of quarry waste, which was thrown over the cliff edge! The vast area of scree now obscures the underlying Portland Sand and Kimmeridge Clay.

However, at this location look out for fossils, especially the bivalve Myophorella incurva. These were named ‘osses ‘eads by the quarry workers and the large bivalve often cursed for ruining a perfect slab of Portland Stone.

Also, look for gastropods amongst the quart overburden. Aplyxiella portlandica, is a turreted gastropod, which was called the ‘Portland Screw’ by the quarrymen and both internal and external moulds are common fossils. Pleurotomaria lugata is also found in Portland Stone Formation, as are the bivalves, Trigonia manselli and Protocardia dissimilis.

Image top left Aplyxiella portlandica | top right Pleurotomaria lugata |

Bottom left Trigonia manselli | Bottom right Protocardia dissimilis

These molluscs found in the Portland Stone, are usually firmly embedded in the very hard rock. Given how heavy the rock can be, it is recommended to reduce the size of the rock containing your specimen prior to loading the fossil in your rucksack. Several specimens can certainly weigh you down!

Use a decent geological hammer (not a wood working hammer borrowed from grandad’s shed or a cheap import which sends off shards of metal in all directions!) Use a stone chisel and carefully take off surplus rock but trying to keep away from the fossil itself. Finer removal of rock can be done at home. Make sure to wear safety goggles when undertaking this sort of work, whether in the field or back at home.

At West Weares, the overburden is a comparatively safe place to search, provided you don’t attempt to clamber too high. The discarded rocks tumble down to the shore, where the Lower Kimmeridge Clay can clearly be seen. Also visible in the now almost obscured cliff face is the grey-coloured Portland Cherty Series, which forms the upper part of the cliff face, with the Portland Sand forming the slopes beneath.

The Isle of Portland is famed for its large ammonites of the genus Titanites as shown below. These enormous fossils can be seen all over the island, in former quarry men’s front gardens, in walls and especially in the walls of the Heights Hotel and above the entrance to Portland Museum and in the grounds. West Weares is a good place to look, although the scree slopes have been well-searched over the years.

Examples of large Titanite Ammonites Visible around the Isle of Portland

You may well find a complete ammonite, or even a large section of these wonderful fossils but beware! The weight of these is incredible and dragging one back to the car will not be easy. Many have tried and failed. The centres of these huge fossils are rarely intact.

At the base of the section lies the Kimmeridge Clay Formation, upon which the Isle of Portland rests. You can access this area by staying on the coast path from Chiswell as far as Tar Rocks. Have a regard for tides and safety along here.

The Kimmeridge Clay is probably not as fossiliferous here as in other parts in Dorset but you should be able to find a good variety of bivalves and gastropods, with the hope of a

marine reptile bone.

Most of the fossils from the Kimmeridge Clay are washed out by the sea and require no tools for extracting from the sticky clay.

Be warned, however, that the rocks are quite dangerous and you will need clamber over them. Fossils are often found wedged between the rocks, which might well be covered in sea weed.

The Isle of Portland and most other fossil-bearing localities are to be found in this book, which forms a series of fossil collecting guides along the Jurassic Coast of Dorset. Available from Siri Scientific Press priced at £19.99.

About Guest Blogger - Steve Snowball

Steve Snowball spent a total of 35 years working in education; initially as a teacher, then as a headteacher and finally as an education advisor in West Sussex.  He retired to live on the Jurassic Coast of West Dorset, where he was able to pursue his keen interest in collecting fossils and spending time walking his dogs, enjoying landscape photography, oil painting and gardening. Steve is the author of ‘A Guide to Fossil Collecting in England & Wales’ and co-author of a series of four other highly-acclaimed guides to fossil collecting on the Dorset coast, all published by Siri Scientific Press.