CHRISTMAS OFFER Subscribe to Dorset Magazine today CLICK HERE

Portland Stone, Jurassic Coast, Dorset

PUBLISHED: 14:47 16 June 2011 | UPDATED: 19:33 20 February 2013

Portland Stone, Jurassic Coast, Dorset

Portland Stone, Jurassic Coast, Dorset

Between Devon's Triassic beds and the Cretaceous cliffs of Ballard Down, much of Dorset's Jurassic Coast consists of Portland and Purbeck limestone.

Portland Stone

Between Devons Triassic beds and the Cretaceous cliffs of Ballard Down, much of Dorsets Jurassic Coast consists of Portland and Purbeck limestone. This has been sourced for building as far back as Roman times. Rufus Castle above Church Ope Cove was constructed from Portland stone in the 11th century, Inigo Jones used it for the Banqueting House in London in 1620, and Sir Christopher Wren followed close behind. Wren, who was born at East Knoyle, about five miles from Shaftesbury, continually specified stone quarried on the Isle of Portland for his rebuilding of St Pauls Cathedral, and subsequently many of the finest buildings in London and other major cities have used Portland stone. Here in Dorset, it has been used by local Isle of Portland people for their own homes, churches and public buildings.

What is Portland stone?
Portland is on the southern side of a dome-shaped fold in the limestone rocks called the Weymouth anticline. These sedimentary rocks were formed in Mediterranean conditions, between 155 and 140 million years ago, when minute fragments of dead sea creatures shells and organic debris sank into the sea-bottom mud where calcium carbonate, or calcite, built up around them. Over time, the immense pressure from overlying rocks and earth movements cemented the whole into Portland limestone. Portland stone isnt all the same, I hasten to add. Some layers produce much better building materials than others, and you will see the various types as you follow the Portland walk.
The best building-material beds are the Whitbed and Basebed limestones, each being about 2m-deep layers of fine-grained freestone. Whitbed can be cut easily in any direction, both are excellent for fine-detail carving and both are very durable, although Whitbed is slightly more weather-resistant than Basebed. At the north of Portland, where we will be walking, the Whitbed is covered by deep layers of Roach and Purbeck rubble, which have to be removed before the better stone can be quarried. The Roach is full of holes and fossils of the Portland Screw, so it is only really suitable for rock armour coastal defences. The Purbeck rubble, above the Roach, is only suitable for dry-stone walling.
Between the Whitbed and the lower Basebed, there is a layer about 1m thick of sandy and shelly curf and chert, which also has to be discarded, often piled high for back-filling but historically dumped over the sea-cliffs. Continuing below the Basebed are the 50m deep Cherty Beds (used only for crushed aggregate), 35m-deep Portland Sand and, visible as you walk above West Weares, Kimmeridge Clay just above sea-level.


More from Out & About

Friday, December 7, 2018

This easy walk takes us into Hardy territory as well offering some glorious views towards Weymouth and Portland

Read more
Thursday, November 29, 2018

Here are some Dorset walks, easy and challenging, to get you out and about over the festive period

Read more
Wednesday, November 28, 2018

If you’re willing to brave the cold this Christmas Day, check out Dorset’s festive swim calendar for the best organised dips taking place in 2018

Read more
Thursday, November 15, 2018

Confusion reigns on the county’s eastern border

Read more
Thursday, November 15, 2018

From festive light switch-ons and Santa’s Grottos, to German Christmas markets and late-night shopping, we’ve covered what’s on in Dorset this season

Read more
Monday, November 12, 2018

From your first step, you will see superb views from hilltops and farmland footpaths on this walk

Read more
Sunday, November 11, 2018

Martin Clunes and his family have called West Dorset home for over two decades. Here he shares some of their favourite local places

Read more
Monday, November 5, 2018

To mark the centenary of the end of World War One we visit some of the memorials erected across Dorset to remember the fallen in the ‘war to end all wars’

Read more
Friday, October 26, 2018

This lovely walk takes us from watercress beds to a church famous for its life-size carvings of apostles

Read more
Thursday, October 25, 2018

Autumn is a great time to brush up on your gardening knowledge with the help of some experts, as well as see some well known gardens in a different light

Read more
Wednesday, October 24, 2018

The guide to Dorset’s best firework displays and bonfire events happening in 2018

Read more
Tuesday, October 23, 2018

Prepare to experience the paranormal this Hallowe’en as Visit Dorset reveals some of the county’s most haunted pubs, stately homes, historic buildings and tanks

Read more
Monday, October 15, 2018

Dorset villages are some of the most beautiful in England – think winding lanes, thatched cottages and a cosy pub or welcoming tea room. We suggest ten of the prettiest villages to visit in the county

Read more
Friday, September 14, 2018

Follow in the footsteps of the Romans on this lovely walk that takes in rare habitat, ancient woodland and glorious views

Read more
A+ South & South West

Newsletter Sign Up

Sign up to the following newsletters:

Sign up to receive our regular email newsletter

Our Privacy Policy

Topics of Interest

Subscribe or buy a mag today

subscription ad

Local Business Directory

Property Search