geology | Collections in the Landscape

Some geology additions to the Buxton collections show volcanic events in the making of the local geology and gave a great excuse (as if one was needed!) to get out and explore to see where they came from. Some of the new specimens came from Cressbrook Dale, a dramatic limestone dale near Litton dominated at the top end by the imposing Peter’s Stone. At various times there’s been volcanic activity at a number of centres in the White Peak, which include Tunstead, Matlock, Alport and Eyam Edge. Not necessarily large volcanoes, these could have been areas of vents and fissures under the shallow sea that covered the area at the time, and from which lava flowed or material was ejected to produce falls of ash. This led to layers or intrusions of lava flow and tuff inside the limestone.

In Cressbrook Dale these outcrop where the rocks have been worn away.

The picture above shows the North end of Cressbrook Dale and another feature of limestone dales – the seasonal river produced by our recent heavy rains!

Standing above the valley on a cold, damp, windy January day, it takes a real leap of imagination to picture the area as it was over 300 million years ago – not here, but thousands of miles away near the equator, covered with a warm shallow sea. Could it have looked like this …?

Cressbrook Dale lava.

Tuff is formed from volcanic ash blown out of vents, eventually settling on the sea bed. There’s evidence that the Litton Tuff was the result of at least two volcanic vents, one west of Tideswell and another under Bleaklow, which probably erupted repeatedly to build up a layer of material.

Litton Tuff from Cressbrook Dale.

Tuff from Peter Dale Vent with limestone fragment.

At Cressbrook Dale the tuff layer forms a ‘wayboard’ separated by a depth of limestone from a lower layer of lava. The picture below shows such a wayboard in Ecton Copper Mine, where the ash appears as a soft clay.

The horizontal ledge shows the sea floor at the time with ‘wayboard’ of volcanic ash above.

Reference:

Hunter J. & Shaw R. 2011 The Cressbrook Dale Lava and Litton Tuff between Longstone and Hucklow Edges, Derbyshire. Mercian Geologist 17(4); 229-242.

In this post Derbyshire Museums Manager, Ros Westwood, introduces a new partnership with Treak Cliff Cavern and Buxton Artclubs Artbox, supporting Made in Derbyshire.

In one of my earliest conversations with my mother-in-law she told me how much she loved Blue John, the unique blue, purple, yellow and white stone from just two mines above Castleton in the Hope Valley. So she is very envious that I look after the Buxton Museum collection. The ornaments which bring ‘oohs!’ and ‘aahs!’ from visitors, include the silver mounted milk pail – surely a sugar bowl? – dated 1803, and the narrow window attributed to John Tym from the middle of the 19^th century, as well as unworked specimens, some huge boulders and many small hand specimens (not all of which are pretty!)

Silver-mounted ‘milk pail’, made from Blue John, dated 1803

So if anything is ‘Made in Derbyshire’ it must be Blue John. Formed within the limestone, Blue John is a fluorite. It is not very hard (only 4 on Moh’s Scale of hardness). The cubic crystals grow in veins through which the distinctive purple and blue layers alternate with white and yellow, providing zig- zag stripes of various intensities. This colour combination makes it attractive for ornaments and jewellery despite being quite a fragile material. There are many ideas of how the colour comes into the stone, whether this is impurities within the fluid, the introduction of hydrocarbons or the occurrence of radioactivity. None really satisfy the mineralogists, yet!

A piece of unworked Blue John from the museum collections

Recently, the museum was offered the opportunity to commission an artwork as part of the Made in Derbyshire campaign. What better suggestion then to explore a commission of worked Blue John to be included in the museum’s new displays. I invited Vicky Harrison of Treak Cliff Cavern with Gary Ridley and Jack Mosley to discuss the possibilities while looking at the museum’s collection, particularly the unworked Blue John, and then artist Caroline Chouler -Tissier and I went over to Treak Cliff Cavern. It was one of those amazing autumn days and the view as we walked up to the cavern of the Hope Valley was spectacular, in the warm October sunshine.

The view from Treak Cliff Cavern

The view from the workshop was equally captivating, but soon we were deeply interested in learning how Blue John is worked, taking a friable material and making it into artefacts as thin as glass.

In the workshop

Caroline and I were taken through the Cavern, and chanced to see the amazing Witch that flies through it as well as the newly discovered Ridley vein of Blue John, named for Gary Ridley. Meanwhile we discussed our ideas and plans.

To celebrate several events – Made in Derbyshire; Collections in the Landscape and even as an advance 125^th birthday present for Buxton Museum (in 2018), the museum is commissioning two exciting new pieces of worked Blue John for the collections. Importantly, much of the work will be made by people under 25, a chance to learn about geology, engineering, art, and something unique to Derbyshire, all at one time.

Jack has been asked to turn a new chalice for the museum, made from the Ridley vein. Jack has been working Blue John for three years, and this exciting commission will mean his work will be in the museum collections for all to see. We hope to film him making of it.

Jack at work

Meanwhile we will work with members of Buxton Artbox Artclubs to make the first Blue John window for over 100 years, following in the creative imagination of John Tym. The Artbox members will visit the cavern and help in the workshop to select material for slicing and polishing. Supported by their artist-in-residence, Caroline, they will suggest ideas of what the finished window may look like. Here at the museum we will look in the vaults at some of the specimens which outwardly look very dull which may find a new life in the window

This will be an exciting creative programme with lively input from many young people. Its early days yet, and everyone is very excited to get things on their way. We will keep you updated through the Collections in the Landscape blog as the work takes shape. We may need your help to wet-and-dry the Blue John slices – Vicky tells us its takes a long time, but it could be good fun!