Scottish ‘Red pebbles’

[Prime586]

As has been said, ballast in S Scotland is often the red igneous rock from Cloburn quarry, and very attractive it is too - and hard-wearing. It is not granite (whatever they claim) which has to contain quartz, feldspar and mica.

According to the British Geological Survey, the igneous rock from Cloburn Quarry is Felsite, specifically Midland Valley Siluro-Devonian Felsic Intrusion Suite Felsite (the quarry produces both red and blue Felsite). That particular formation of Felsite only exists in the quarry and a narrow seam on the other side of the A73 under Shawhill Wood.

From the 2024 Planning Application to extend the quarry:
"The site is located on Cairngryffe Hill and quarrying has been on-going at this location since 1896. Previously the site was operated as two independent quarries: Cairngryffe Quarry, located to the south-west, being operated under leasehold by Strathclyde Regional Council and Cloburn Quarry, which was worked under a lease by Tilcon Ltd. In 1982 Cloburn Quarry was acquired by the current owners who then acquired Cairngryffe in 1987 and bought out the leasehold. From this point the two quarries have been worked as a single unit, the quarries merging as the rocking forming the barrier between the two sites was extracted.

The deposit was initially worked as a source of railway aggregate, where it was discovered that the inherent strength of the felsite was ideal in the construction of railway tracks, providing engineers with a durable track ballast material that could be relied upon to be extremely hard wearing, thus ensuring a long lasting maintenance free track.

Moving further into the 20th century, Cairngryffe Quarry became a very important source of material for the local road building industry. Lanark County Council, who operated the quarry during this innovative period in road construction, were at the forefront of new highway surfacing technologies. They discovered that using these aggregates in both macadams and asphalts provided a hard wearing and resilient product that was ideal for
the surfacing requirements of now heavily trafficked roads. Through time, the quarry became synonymous with road construction due to the instantly recognisable red roads that would greet any visitor to Lanarkshire and, as a testament to the aggregate, can still be seen today in many rural parts of the surrounding area.

Today Cloburn Quarry still plays an important part in the country’s rail network. It is the main Scottish supplier of Network Rail approved track ballast to the UK market. It consistently produces a low attrition rail ballast required to meet the strict specifications. During the COVID pandemic Cloburn was deemed an essential supplier to Network Rail. Indeed, it is considered to be part of Network Rail’s strategic supply chain for track ballast and other specialist rail products. In 2020, Cloburn Quarry Company invested in a railhead at Ravenstruther (previously operated by Scottish Coal) and this now provides a direct link onto Network Rail’s West Coast Mainline."

 

[AndrewE]

The latter is known as "red blaes", and may be what the OP has seen on platforms or walkways - not suitable as ballast. Traditional material for "all-weather" football pitches, but not good to fall on! See https://www.brewsterbros.com/products/shale-blaes/

https://www.bbc.co.uk/news/articles/cwyr5w6xe12o is the second time I have heard "Blaes" - and both within a week!

For the past six months, Brian Kennedy has been living next to an underground fire burning at temperatures of up to 500C.

From the road, the houses on Burleigh Street look like normal west of Scotland homes.
But at the rear there's a wooded area where last summer fires broke out deep beneath the ground, sending smoke billowing into the air and causing residents to fear for their safety.

Experts eventually discovered an underground fire fuelled by oil shale which had been used in the building of a long-gone railway line 120 years ago.
It's unclear what started the fires, but to put them out, workers had to remove tonnes of "molten lava" from deep below the surface.

Maybe in 1900 the shale stills didn't extract all the oil? I'm still surprised that the track sub-base at the bottom is burning. I can't get the NLS historic maps to line up with today's road to find if there was a cutting, there are loads of coal mines and iron works, which presumably have been erased for the current town to be built. (I'm assuming it isn't actually oil shale bedrock burning.)

 

[InOban]

According to the British Geological Survey, the igneous rock from Cloburn Quarry is Felsite, specifically Midland Valley Siluro-Devonian Felsic Intrusion Suite Felsite (the quarry produces both red and blue Felsite). That particular formation of Felsite only exists in the quarry and a narrow seam on the other side of the A73 under Shawhill Wood.

From the 2024 Planning Application to extend the quarry:
"The site is located on Cairngryffe Hill and quarrying has been on-going at this location since 1896. Previously the site was operated as two independent quarries: Cairngryffe Quarry, located to the south-west, being operated under leasehold by Strathclyde Regional Council and Cloburn Quarry, which was worked under a lease by Tilcon Ltd. In 1982 Cloburn Quarry was acquired by the current owners who then acquired Cairngryffe in 1987 and bought out the leasehold. From this point the two quarries have been worked as a single unit, the quarries merging as the rocking forming the barrier between the two sites was extracted.

The deposit was initially worked as a source of railway aggregate, where it was discovered that the inherent strength of the felsite was ideal in the construction of railway tracks, providing engineers with a durable track ballast material that could be relied upon to be extremely hard wearing, thus ensuring a long lasting maintenance free track.

Moving further into the 20th century, Cairngryffe Quarry became a very important source of material for the local road building industry. Lanark County Council, who operated the quarry during this innovative period in road construction, were at the forefront of new highway surfacing technologies. They discovered that using these aggregates in both macadams and asphalts provided a hard wearing and resilient product that was ideal for
the surfacing requirements of now heavily trafficked roads. Through time, the quarry became synonymous with road construction due to the instantly recognisable red roads that would greet any visitor to Lanarkshire and, as a testament to the aggregate, can still be seen today in many rural parts of the surrounding area.

Today Cloburn Quarry still plays an important part in the country’s rail network. It is the main Scottish supplier of Network Rail approved track ballast to the UK market. It consistently produces a low attrition rail ballast required to meet the strict specifications. During the COVID pandemic Cloburn was deemed an essential supplier to Network Rail. Indeed, it is considered to be part of Network Rail’s strategic supply chain for track ballast and other specialist rail products. In 2020, Cloburn Quarry Company invested in a railhead at Ravenstruther (previously operated by Scottish Coal) and this now provides a direct link onto Network Rail’s West Coast Mainline."

OT but I believe SNCF gets their ballast from Glensanda super quarry on the West Coast of Scotland!

 

[Morayshire]

https://www.bbc.co.uk/news/articles/cwyr5w6xe12o is the second time I have heard "Blaes" - and both within a week!

Maybe in 1900 the shale stills didn't extract all the oil? I'm still surprised that the track sub-base at the bottom is burning. I can't get the NLS historic maps to line up with today's road to find if there was a cutting, there are loads of coal mines and iron works, which presumably have been erased for the current town to be built. (I'm assuming it isn't actually oil shale bedrock burning.)

If you use NLS's georeferenced maps option, you will find that the section in question is an embankment.

 

[Prime586]

https://www.bbc.co.uk/news/articles/cwyr5w6xe12o is the second time I have heard "Blaes" - and both within a week!

Maybe in 1900 the shale stills didn't extract all the oil? I'm still surprised that the track sub-base at the bottom is burning. I can't get the NLS historic maps to line up with today's road to find if there was a cutting, there are loads of coal mines and iron works, which presumably have been erased for the current town to be built. (I'm assuming it isn't actually oil shale bedrock burning.)

If you use NLS's georeferenced maps option, you will find that the section in question is an embankment.

Link to the NLS side by side map viewer showing the section of the old embankmant (the wooded area behind the houses on Burleigh St). that caught fire and was dug out .The cleared area visible immediately to the south on the satellite view was the site of 11 4-storey blocks of flats from the 1960s that wrre demolished in 2022.

The embankment was built in the 1870s to carry the Whifflet to Bothwell Junction section of the Glasgow, Bothwell, Hamilton and Coatbridge Railway (part of the NBR) through the area and it's connection to the NBR's mineral line network that connected to widespread workings of Rosehall Colliery. There had been a number of shale oil works in the vicinity of Coatbridge that had all gone out of business by the beginning of the 1870s, so the spoil tips from these works may have been used to build the embankment.

It was not just oil shale that was found to be burning. As the site was excavated, burning coal waste was found too. The area between the embankment and the river had been used as a spoil tip by Rosehall Colliery, and at some point after the line opened the srea where the flats were later built had also been elevated to build an 11-track set of sidings alongside the embankment, and the embankment itself had been widended to provide an access spur for the sidings. Presumably spoil from Rosehall Collery had been used in the construction.

 

[AndrewE]

Link to the NLS side by side map viewer showing the section of the old embankmant (the wooded area behind the houses on Burleigh St). that caught fire and was dug out .The cleared area visible immediately to the south on the satellite view was the site of 11 4-storey blocks of flats from the 1960s that wrre demolished in 2022.

The embankment was built in the 1870s to carry the Whifflet to Bothwell Junction section of the Glasgow, Bothwell, Hamilton and Coatbridge Railway (part of the NBR) through the area and it's connection to the NBR's mineral line network that connected to widespread workings of Rosehall Colliery. There had been a number of shale oil works in the vicinity of Coatbridge that had all gone out of business by the beginning of the 1870s, so the spoil tips from these works may have been used to build the embankment.

It was not just oil shale that was found to be burning. As the site was excavated, burning coal waste was found too. The area between the embankment and the river had been used as a spoil tip by Rosehall Colliery, and at some point after the line opened the srea where the flats were later built had also been elevated to build an 11-track set of sidings alongside the embankment, and the embankment itself had been widended to provide an access spur for the sidings. Presumably spoil from Rosehall Collery had been used in the construction.

Thanks, that's all very helpful.
I do remember that big blocks of coal is what they wanted back then so a lot of small coal was just dumped, either underground (inside the mine according to the guide at Dudley) or with other spoil.

 

[Port Road]

OT but I believe SNCF gets their ballast from Glensanda super quarry on the West Coast of Scotland!

Slightly off topic - the base of the Statue of Liberty in New York is made of red sandstone from Locharbriggs quarry outside Dumfries, and much of the Victoria embankment in London is made from Dalbeattie granite.....

 

[LickeyIncliner]

Maybe in 1900 the shale stills didn't extract all the oil?

I'd be quite certain they didn't. I've read that even modern gold processing doesn't get 100% of the metal out of the rock, despite its value. I'm sure oil shale processing was fairly ineffective in the 1870s. Or earlier - the shale in question might have been processed decades before the blaes were used to build the embankment. Also, @Prime586 says the Coatbridge refineries had closed by then; there might well have been stocks of unprocessed shale that weren't worth transporting to a still-working refinery. Any such stocks might well have gone into the embankment too, either by accident or because someone judged it was sufficiently inert. If someone did make that judgement, it was right for a century and a half...

Which raises the question: why now ? Has the fire been slowly burning for years and just didn't become apparent until mid-2025, or did something happen then which allowed the fire to start, e.g. by allowing oxygen in to mix with gases given off from the remaining oil? (I admit this is largely a question for some other forum - but "what can go wrong with 150-year old railway embankments" seems relevant here...)

 

[DelW]

Which raises the question: why now ? Has the fire been slowly burning for years and just didn't become apparent until mid-2025, or did something happen then which allowed the fire to start, e.g. by allowing oxygen in to mix with gases given off from the remaining oil? (I admit this is largely a question for some other forum - but "what can go wrong with 150-year old railway embankments" seems relevant here...)

The BBC article linked from post #32 says that the cause is unknown (my highlighting):

Experts eventually discovered an underground fire fuelled by oil shale which had been used in the building of a long-gone railway line 120 years ago.

It's unclear what started the fires, but to put them out, workers had to remove tonnes of "molten lava" from deep below the surface.

One of them was Stewart Browne from engineering firm WSP.

Using geothermal imaging and 100-year-old maps, he discovered the area behind Burleigh Street was once a railway. When it was built, oil shale was put into the ground.

Oil shale, or blaes as it is sometimes known in Scotland, is a material that was historically mined from the bedrock.

It's not clear why 120 years later the material set alight.

 

[michael769]

Underground fires usually involve exothermic chemical reactions (for example Lithium, Sodium and Potassium can all produce a lot of heat when they come into contact with water), which generates enough heat to ignite nearby combustible materials - for such a fire to become self sustaining it needs a source of oxygen - as it happens there are lots of molecules that release oxygen when heated and a fair few are quite abundant underground - hence why deep mining is so terribly dangerous.
In most cases it's not really a "fire" as we'd normally understand such a thing but more of a smouldering mass producing a lot of heat and pollution without any actual flame - the latter when it eventually percolates to the surface leads to it's discovery.

Depending on the geology such masses can indeed smoulder away for decades or even centuries and oftentimes by the time it is excavated the original trigger will have been long consumed. There are likely many such masses underground both natural and man made that are never discovered.
The reason underground fires often take months or years to deal with is that as well as the risks associated with the fire - such masses can release toxic gas and require continual careful monitoring.

 

[Pigeon]

You don't find native alkali metals hanging around underground waiting to react with some water. Nor (in general) do you find substances that release oxygen when heated. Anything that reactive will have reacted long ago.

What you do often find, especially mixed with deposits of organic origin, are pyritic substances - the clue is in the name - which can react with atmospheric oxygen when the ground is disturbed to allow it access, and generate heat which builds up until something carbonaceous ignites. This is famously what happened to the Wolverton embankment during its construction due to something not far removed from pond slime being used as fill material. Decaying organic material can also release phosphine which ignites spontaneously on contact with air, although I think the Wolverton fill was long past that stage. Human activities can also cause ignition, for instance if a bonfire ignites an outcropping coal seam; this is probably what happened at Centralia.

The fire then burns using atmospheric oxygen, tenaciously because there is a large mass to retain the heat, but slowly and dirtily because the oxygen supply is limited.

Coal mining is dangerous because coal seams release methane which can form an explosive mixture with air. Furthermore an explosion can spread far beyond the actual pocket of methane due to the blast wave stirring up coal dust into the air which then itself burns in a dust explosion. In hard rock mining the atmospheric dangers are much less and of an entirely different nature, since there aren't any sources of explosive gases around, but you may run into pockets of depleted oxygen and in the long term radon inhalation may be a problem.