Discovering The Isle of Portland along the Jurassic Coast of Dorset

Fossil Coast in collaboration with Matt Pinner one of Dorset's leading professional landscape photographers explores the rugged and picturesque Isle of Portland on Dorset's Jurassic Coast and a location whose landscape inspired Dorset born writer Thomas Hardy.

Portland Bill Light House - Image by Matt Pinner

Thomas Hardy described the Isle of Portland as, “the peninsula carved by Time out of a single stone” and whose weekly serialised story "The Pursuit of the Well-Beloved" in 1892 followed the protagonist, a sculptor named Jocelyn Pierston, who had returned to the "Isle of Slingers" - we shall revisit this expression later.

From my own personal point of view The Isle of Portland is among my most favourite places to visit in the UK. A good day is having an ice cream with friends and family sitting by the most southerly point of Portland Bill Lighthouse looking out to sea onto the toil and trouble of the tidal cauldron known as the "Portland Race".

The Isle of Portland was where we as a family learnt to sail at the Weymouth and Portland National Sailing Academy on Osprey Quay. Also, I can highly recommend walking the Portland loop of the South West Coast Path a 13Km trail around the island. Still, one of the best viewpoints of the Isle of Portland in profile is from the cliffs from Durdle Door several miles to the east.

Pulpit Rock - Image by Matt Pinner

The Isle of Portland is 6Km in length and approximately 3Km in width and at its highest point on Verne Hill is 149 metres above sea level. The coastline of the Isle of Portland is designated as a Site of Special Scientific Interest (SSSI) and part of the Jurassic Coast.

The Isle of Portland is however not an island per se but rather a tied-island connected to the mainland by a tombolo of shingle known as Chesil Beach behind which lies a lagoon called the Fleet.

Chesil Beach and the Fleet area was the inspiration for the 1898 novel called "Moonfleet" written by J. Meade Falkner about a tale of smuggling, treasure, and a shipwreck set in 18th-century England.

Visit the Portland Museum for more information about the fossils found on the Isle of Portland.

Putting the Oo into Oolith

The history of the Isle of Portland is closely bound to its stone industry and specifically the hard and durable Portland Stone used by the likes of Sir Christopher Wren to rebuild St. Paul’s Cathedral after the Great Fire of London in 1666.

Image by Joel & Jasmin Førestbird

Portland Stone or oolitic limestone (oolite is Greek for "roe-stone" or "fish roe") was accumulated on the coastal shelf during the late Jurassic.

It is this limestone that in part has inspired the creation of our Lime Stone London Dry Gin.

In the UK there are several types of Oolites including the Great or Main Oolite known as Bath Stone and the Superior Oolite known as Portland Stone. Throughout history Oolite has been quarried and used as building stone.

An Oolite is a spherical crystalline deposit of billions if not trillions of small concentric or radial structures called “ooliths”. These are composed mainly of calcium carbonate surrounding a nucleus of a sand grain or a tiny shell fragment.

The Portland Group

The hard sedimentary rock of the Isle of Portland forms what is known as the Portland Group whose upper layers are predominantly limestone including freestones and the lower part is predominantly argillaceous (clay rich), dolomitic sandstones; some shales, and thin beds or nodular layers of micrite.

This group was deposited in a warm tropical marine environment around 145-164 million years ago during the late Jurassic period known as the "Tithonian Stage". Marine reptiles such as pliosaurs and ichthyosaurs would have swam these seas, though their remains are rarely encountered in this stone.

The Tithonian, is a name derived from the Greek mythological figure Tithonus, who was the consort of Eos (Aurora), goddess of the dawn, overlies the Kimmeridgian Stage and underlies the Berriasian, the lowest stage of the Cretaceous Period.

Portland's Rifting and Uplifting

Looking from North to South it is evidently visible that the Isle of Portland has experienced considerable movement, rifting and uplift over a geologic timeframe. The layers of rock or strata on the Isle of Portland gently dip southwards until its flank submerges offshore into Shamble Syncline off Portland Bill.

Image by Wikiwand - The Isle of Portland looking North (Left) to South (Right)

The Isle of Portland is part of the Weymouth anticline and it is this structure that gives the island its distinctive wedge or ramp shape. The Weymouth anticline is a convex fold of several rock layers that have been deformed as a result of a broader system of geological disturbances from orogenic processes or mountain building events that extend across the south of England, the English Channel and into northern France.

The Isle of Portland Fossils

Among the diverse fossil record for the Isle of Portland are Jurassic patch‐reefs, coastal sabhkas, fossil forests, dinosaur footprints and a sedimentary shelly beach layer known as the Portland Admiralty Roach a coquina almost entirely composed of fossilised mollusc or gastropod shells and shell fragments. Many of the larger fossils are now exhibits across the Isle of Portland and are very rare to find. (Note: A Sabhkas is an Arabic word for a coastal supratidal mudflat or sandflat in which evaporite-saline minerals accumulate.)

West Weare in the north is regarded as a good Kimmeridge Clay fossil hunting location on the Isle of Portland. Not only does the Kimmeridge Clay cover a considerable area of the seafloor of Portland Harbour and west of the Chesil Beach where ammonites, bivalves and large marine reptiles such as ichthyosaur have been found. The Kimmeridge Clay is also exposed at West Cliff and these fossils may also be found in the slipped Kimmeridge Clay.

Freshwater Bay to the east of the Isle of Portland is another good place both on the cliff top and beach foreshore to fossil hunt amongst the Portland Sand and Limestone. A combination of trace fossils of algal laminations, fossil tree trunks, bivalves and gastropod can be found.

Among the highlights of the Portland Stone is an oyster called Liostrea expansa; a trigonid saltwater clam called Laevitrigonia gibbose colloquially known as a "horses head" and moulds of aragonitic fossil shells, particularly the "the Portland Screw", a turreted gastropod called Aptyxiella portlandic. Unfortunately, the large ammonites Titanites (both anguiformis and giganteus) from the Portland Freestone Formation are now rarely found.

Finally, getting back to the "Isle of Slingers" reference. Hardy's portrayal for the Isle of Portland as the ‘The Isle of Slingers’ is actually an old name for Portland Island – given to it because of the habit of the local population to hurl stones at unwanted visitors – or "kimberlins" or ‘foreigners from the mainland of Wessex’.