Portland’s Geology.

Portland’s dramatic landscape is shaped by the stresses placed upon it by the Weymouth Anticline, a huge fold thrown up during the mountain building period that created the Alps when the continents of Africa and Europe collided around 30 million years ago. The uplifting process tilted the Isle and created cracks and gullies that shape the towering cliffs to the west and the boulder strewn landslides in the east. The uplifting of Portland has tilted the Isle so the cliffs on the west side are higher than those on the east. This means the western cliffs erode in a completely different way from those on the opposite side. The cliffs of East Weare are subject to large sprawling landslides, such as the Great Southwell Landslip, where the cliffs have fallen “down dip”, while the cliffs on the western side of the Isle tend to topple into the sea where they have fallen “up dip”. All the falls and slides on either side of the island are parallel, following the cracks and fissures created

Chesil Beach Underwater

Underwater the structure of the Chesil Beach descends in a series of steps and eventually bottoms out at around 12 meters.

Pebble Size and Longshore Drift

The stones that make up the Chesil Beach are mainly derived from East Devon, consisting of Metaquartzites of the Ordovian and Devonian Age, Chert and Flint. A unique feature the Chesil Beach is how the pebble size changes from one end to the other. Large cobbles are found at Chesil Cove, Portland, while West Bay has fine grit and gravel. It is thought the bigger heavier stones have a larger surface area and are therefore carried further to the east by the powerful prevailing south westerly waves hitting the beach at an angle, while the smaller lighter stones are carried back to the west by the less powerful waves approaching from the south east. In effect the stones zigzag their way along the coastline, carried by this longshore drift, accounting for the size graduation. The harbours at Lyme Regis and West Bay are both obstacles to the longshore drift, and the reduction in quantity of stone being delivered through coastal erosion in East Devon is diminishing. The long-term future

The Chesil Beach (Chesil Bank)

Consisting of a 100 million ton bank of pebbles, the Chesil Beach stretches for 28 km to West Bay. The beach varies between 36 and 200 meters wide and also in height, being 14 meters at Portland and just 5 meters at West Bay. The bank of pebbles separates the sea from Britain’s largest tidal lagoon, the Fleet, an important wildlife habitat for all manner of extraordinary flora and fauna. The beach is marching inland at a rate of 5 meters every century, reducing the size of the Fleet Lagoon in the process. The Chesil Beach is by no means stable. Storm waves have breached its pebble bank several times in the past, flooding the Fleet Lagoon, the land behind it and Portland to a depth of several meters. In one great storm the beach was swept away, exposing the underlying Kimmeridge Clay, in which were coins, jewelry and all sorts of artifacts that had been lost between the pebbles throughout the centuries.

Chesil Cove Marine Life

Diving off Chesil Cove shows the underwater structure of the beach. It goes down in steps and eventually bottoms out at around 12 meters. A rocky reef gives way to flat sand, where inquisitive cuttlefish can often be found, hunting for sandeels.

The Spirit of Portland

A statue and derrick alongside the main road to the top of Portland from Fortuneswell stands to remind us of what Portland’s past was built on, the industries of fishing, quarrying and stonemasonry.

The Chesil Beach and Smugglers

Folklore says that a local fisherman or smuggler could tell exactly where he was on the beach at night or in fog simply by looking at the size of the pebbles. This aided him in sneaking ashore, away from the customs men and their patrols.

The Portland Estate

Around 250 hectares of land on Portland are currently managed by the Crown Estate. This is part of the “Royal Manor of Portland” which has been in the of the Crown’s possession since Saxon times. Around 160 hectares of the Estate is common land, which was traditionally used by the locals for the grazing of their animals and the removal of stone. The land is supervised by one of the last surviving Courts Leet in Britain, having been in operation since 800AD. Portland’s Court Leet meets on the third Friday of November every year, when matters involving income derived from fines and rents for the encroachment onto common land can be administered.

The Verne Citadel

Overlooking the Isle’s Northern approaches of Chesil Beach and Portland Harbour is the Verne Citadel, (now Portland Prison). This is an immense 56 acre Victorian fortress built between 1860 and 1874 by the Royal Engineers. Its 21 meter deep defensive dry moat was created by convicts who quarried away 1.5 million tonnes of stone for the outer Portland Harbour breakwater. The Citadel could house up to 3000 soldiers and was originally armed with 9 fixed and 10 mobile artillery pieces. A rear entrance was added in 1881 as access to manning the high angle battery outside the main stronghold. For rifle range practice, the troops used the deep moat from where any stray bullets would find it hard to escape!