Manchester Building Stones
The North West Geologist
|A Building Stones Guide to Central Manchester|
Third Edition (2014)
Four self-guided walks through the city centre
Now available to purchase
Newsletter - December 2015
The full, illustrated newsletter is available as a pdf for download.
Text extracts are given below.
Lion Salt Works Restored to Life
Soon after I began to study geology, in 1997, Alison Scott arranged a visit to the Lion Salt Works at Marston, near Northwich. I went along to see what remained of the dilapidated buildings of the works, which ceased production in 1986, and to discover how table and cooking salt had been produced from brine by the 'open pan' method. The buildings were Grade 2 listed in 1986 and designated a Scheduled Monument by English Heritage in 2002. Since then I have driven past the boarded-up site many times and reflected on what a further ten years of decay had inflicted on the site. In 2008, after much research and hard work, funding was secured to restore the Lion Salt Works as a museum; at a cost of £10m. Restoration work began in July 2009, was completed in September 2014, and the Works re-opened in June 2015 (Ref. 1).
On 4th November 2015 Marketing Cheshire (of Chester and Cheshire West Council) organised a 'Geology Event' at the Works especially for geologists (referred to in the press release as 'Rock Stars'! Ref. 2) representing organisations both locally and nationally. I was delighted to represent the MGA along with Past President, Peter del Strother. It was also encouraging to meet a group of enthusiastic geology pupils, with their teacher, from Calday Grange Grammar School in the Wirral.
We were introduced to the complexities of the restoration with a laser-generated fly-through video. Because of the poor state of the buildings (some were held up only by the strength of the roof) they were too dangerous for surveyors to enter. This was quite remarkable and emphasised the care and skill needed by all those involved in the works to bring the project to a safe conclusion. It is the first restoration project in the country to adopt this technique.
We were split into two groups for a guided tour of the site. The exhibits cover the social as well as the working aspects of the 'open-pan' method of salt production; you pass through the Red Lion pub that was built on site for the workers. Every effort has been made to re-create the 'humid working atmosphere' in the sweltering rooms where the brine was boiled in open, iron pans. The salt was scraped to the sides to be collected and put into wooden containers to be dried.
There are exhibits of the drying, cutting and grinding the salt blocks. Hands-on demonstrations of crystallising salt as well as models and sections showing the geology of the strata comprising the salt beds.
A major part of the museum is devoted to the disastrous effect that wild-brine pumping had on ground stability and the resulting impact on houses, roads and the salt mines themselves. The 'flashes' are sunken areas filled with water where the land collapsed into the mines. It concludes with the positive outcome of the new habitats and nature reserves that have been reclaimed from what was once an industrial wasteland.
An interesting, two minute, aerial film of the Lion Salt Works is available here. (This link is free to download and to embed on websites, courtesy of M7Aerial and Marley Eternit).
The museum is an impressive reconstruction and representation of the original 'open-pan' method of salt production. It brings home what an important raw material salt has been, and still is, in everyday life. In conversation with Professor Christopher Jackson of Imperial College, (a former Manchester SEAS student) who now specialises in salt tectonics, he remarked that 'salt comprises just 1-2% of the sedimentary succession, but forms the seal for all the major oil and gas reservoirs in the world'. Without doubt you will find a visit full of interest and wonderment at the toils and tribulations that were endured to bring us that essential additive to our diet, especially our fish and chips!
Continuing the heritage of salt theme, there is another Cheshire initiative called 'Saltscape'. It is a new partnership to protect, enhance and celebrate the unique landscape of the Weaver Valley by connecting heritage, nature and people to the legacy of Salt. It has funding of £1.4m from the Heritage Lottery Fund, spread over three years, to achieve its aims. One of the partners is Cheshire RIGGS involving Professor Cynthia Burek, of the University of Chester. I have become involved as a committee member of the Northwich and District Heritage Society and have agreed to lead a geology walk round Frodsham for Saltscape in May next year. Further details can be found at the Saltscape website, where the full 2016 programme of events will be published shortly.
1. Hewitson, Chris, 2015, The Open Pan. The Archaeology and History of the Lion Salt Works. West Cheshire Museums. ISBN 978-0-9932835-0-5
2. Marketing Cheshire, 6 November 2015. Press release "'Rock' stars praise new £10m Lion Salt Works"
Joint MGA/Lancashire Trip to the Wirral
Leader: Hilary Davies
Date: 22 June 2015
The purpose of this day was to examine the outcrops of rock on the Wirral Peninsula and learn about the Triassic Period. The Triassic lasted about 50 million years, from 250 to 200 million years ago, when Britain lay at the heart of the single, giant continent of Pangaea at 10-20° north of the equator.
The climate was initially hot and dry. There was no water or vegetation to bind the sediments so it was easily blown about by wind. There were, however, occasional flash floods that moved huge amounts of sediment. To the south of Britain was a range of mountains that were the source of much of the sediment. With time the Triassic climate became less arid; there are preserved footprints of a small dinosaur-like animal in the damper sediment. Recent microscopic research has identified fragments of plant material, but none has been preserved on a large scale. Subsequent earth movements and the erosion of overlying marine sediments have exposed the Triassic sediments on the Wirral which is now a 'saddle' with the youngest rocks in the middle.
The last retreat of glacial ice from the Wirral around 15,000 years ago left glacial till filling the low points in the landscape. Post glacially the Wirral has been modified by rivers and the sea. There is an ancient forest encased in peat, which has been covered and hidden by the belt of migrating sand-hills; until recently backed by lagoons.
Grange Hill (Helsby Standstone)
Opposite the Broken Heart in Abbey Lodge, we examined the texture, grain size and shape of the sandstones. The sandstone is very mottled from red to almost white. The sand grains are well rounded, typical of sand grains blown a long distance by the wind. The grains are coated with haematite. Cross bedding can be seen. The better cemented sandstone is black with pollution; in the softer sandstone there are bee holes.
Red Rocks, Hoylake (Chester Pebble Beds)
There are two types of pebbles. One is a very distinctive, hard, well rounded, pale quartzite. Its source is the mountain range to the south in what is now Brittany. The pebble size becomes progressively smaller with distance from the source; this is their northern limit. The other pebble type is of dark red mud with a rim of sand grains enclosing the mud, known as an 'armoured mud ball'. The mud accumulated in a braided river, back water environment, was baked in a hot climate and then transported a short distance by water. Small scale cross bedding can be seen.
As the name suggests this is the heart of Viking Wirral. From the top of Thurstaston Common there is a panoramic view of the Wirral. The high ground of Thursaston Common is sandstone forming poor farming land. Compare this with the good farming land, of the Cheshire Plain, on the drift which is intensively cultivated. Cheshire cheese is based on milk from cattle grazed on the rich pasture of the glacial deposits. The bed rocks are 15m below the River Dee and dip towards Chester. Ice came down the Irish Sea and was deflected by the Snowdon ice cap inland along what is now the Dee towards the Cheshire Plain. Consequently the River Dee valley is 'too wide' for its present day river so is silting up.
There are differing interpretations for the origin of Thor's Stone. Did the glaciers wear away the surrounding rocks, but not Thor's Stone? Is it residue from quarrying? It seems likely that Thor's Stone supported the crane used in the quarrying of the surrounding hard sandstone; utilised for local building stone. And what is the origin of the narrow channels or troughs running down the stone? Has the Stone been scoured by water flows under the ice? Or are they as a result of generations of children sliding down the slope and wearing these feet sized channels? Victorian postcards show Thor's Stone without the channels, so is the probable explanation.
Road Cutting near the Thursaston Common carpark
This is a long exposure of a significant section of the Triassic sandstones. The lower part is the Wilmslow Sandstone Formation, the Thursaston Hard Member is below, and the Thurstaston Soft Member above. The different layers are picked out on the basis of their relative hardness. The Hard Member is resistant to erosion and has been blackened by pollution. The Soft Member erodes faster and so remains fresh in colour. Both members have very similar grain size and shape as the sand grains at Grange Hill. The cement of the Hard Member is what makes the difference.
A fault plane at this location is picked out by several finely spaced offset creamy white bands in the lower part of the cutting. The fault plane is also creamy white. Faults in rocks tend to act as focal points for the penetration of groundwater which washes out the red, iron-rich staining in the rock.
The cliffs here provide what has been described as the best display of the composition of the Irish Sea glacial till. This is because the cliffs are occasionally undercut by the sea causing them to stay vertical and dry and therefore free of vegetation.
The pebbles in the cliffs and on the beach are from different sources; transported here by the ice from the bed of the Irish Sea, the Lake District and southern Scotland. The till also contains fragments of seashells and gypsum.
There are a number of very large, rounded boulders of a variety of rock types on the beach. One explanation for them is that they were brought here as ballast in sailing ships that beached at the base of an old lime kiln. Once the ships were loaded up, the ballast was no longer required, so was discarded.
Our thanks to Hilary for a very interesting day and excellent handout. Information provided by Hilary Davies has formed the basis of this report.