Snot's troglodytes and rifting continents

 
I was born in Nottingham – some time around the late Pliocene: there’s a plaque somewhere, I’m sure. Nottingham is an old city, founded in Saxon times, when it was known as Snotengaham, the place where Snot’s people lived; it was strategically sited on sandstone bluffs overlooking the river Trent and the Norman invaders would later build their castle there. The city is, of course, best known for the legend  of Robin Hood and his merry men (and, presumably, women), and draws many visitors for that reason. But the castle today is a relatively modern affair (see the bucolic print below, from 1776) and Robin Hood is a brand more than anything else. However, the inquisitive will find evidence of real history that is far more tangible – centuries of excavation into the sandstones beneath the city.

I remember as a kid the famous “Trip to Jerusalem” pub and its rooms and caves carved back into the rock; and the history of the city’s caves came with all the dire, dark, and bloody stories that kids love – dungeons and death, mysteries and evil-doing. Evidence of the subterranean maze can easily be seen from the outside today, entrances in the cliffs frustratingly closed by locked doors and metal grills.

 
This man-made cave system, space hewn from the rock, has developed over the centuries because the sandstone is relatively poorly cemented and easily excavated. At least since Mediaeval times, tunnels and rooms have been carved out for a vast array of purposes, including dungeons, beer cellars, cess-pits, tanneries, malt-kilns, houses, wine cellars, tunnels, summer-houses, air-raid shelters, sand mines, follies, dovecotes and, for while during WWII, the storage of radium. Temperatures underground remained constant and cool, making for ideal conditions for brewing and storing ale – the Mediaeval malt kiln below is an example of the year-round brewing facilities that made Nottingham famous for its beer (a reputation sadly much-diminished).

 
The known extent of this subterranean infrastructure probably only represents a fraction of the entire system, and now a project to survey and map the caves is well-underway, superbly documented on the project website - “The Nottingham Caves Survey is the first part of the Caves of Nottingham Regeneration Project (CoNoRP). This is a two-and-a-half year project funded by the Greater Nottingham Partnership, East Midlands Development Agency, English Heritage, the University of Nottingham and Nottingham City Council. The project intends to take a fresh look at Nottingham’s caves and encourage the City and its visitors to appreciate the caves for the unique historical resource they are.” The survey is based around the wonderful technology of 3D laser scanning, described on the website:

Laser scanners come in a variety of forms but they all work in a similar way. The scanner fires out a beam of laser light which reflects back from the first thing it hits. The instrument measures the amount of time it takes for the light to return, and from this can calulate how far away that object is. The scanner then rotates the beam a little, and takes another measurement. It continues to rotate vertically and horizontally until it has taken measurements in a 360-degree horizontal circle and usually a 310- degree vertical circle. All the measurements are accurate to around +/- 2mm. From these measurements we have an almost complete 3D survey of a cave. What makes this technology really exciting is the speed at which modern laser scanners work - up to 500,000 survey points per second! The resulting ‘cloud of points’ can be connected to adjoining scans to produce complete surveys of cave systems. Once downloaded into the processing software we can do lots of different things with the point cloud data - make simple sections and plans, elevation maps and isometric images, fly-through videos, explorable .mov images, TruView web delivery, and virtual or real models. Because of the accuracy of the survey data, it can also be used for monitoring the caves. We can go back and re-survey a cave after a year or a hundred years and see exactly how and where it has changed.

And the results are dramatic. The strange image at the head of this post is laser-scanned orthographic plan of the Peel Street caves, Nottingham’s largest cave system and a sand mine that was excavated between 1780 and 1820. Here’s an example, showing the caves in the Castle Rock, including the infamous “Mortimer’s Hole,”  Brewhouse Yard caves, and “Ye Olde Trip to Jerusalem Inn” caves (click for full-size image).

The images are stunning, and, on some of the high resolution versions available on the project website, you can begin to see the sedimentary structures:

 
So where did these accommodating sandstones come from? In the UK, they are part of the appropriately named Sherwood Sandstone Group, the outcrops around Nottingham being originally named the Bunter Sandstone; essentially all of them are red. They were deposited in desert and fluvial environments during the Triassic Period a couple of hundred million years ago, and their structures, including beautiful cross-bedding, record flash floods and blowing sand:

 
These photographs, courtesy of Ian West at the University of Southampton, come from the south coast of England where the Triassic Sherwood Group inevitably underpins the Jurassic Coast World Heritage Site. For the Sherwood Group, along with whatever its local equivalents may be in local nomenclature, extends across the UK and into the rest of Europe. The sandstones are often, as they are in Nottingham, poorly cemented and porous and can make excellent reservoirs for water and for oil and gas. But the Triassic sands don’t stop on the south coast of England – they can be found, in all their red glory, down the east coast of North America, where they preserve the first dinosaur footprints ever found (by the wonderfully named Pliny Moody working on his father’s farm in Massachusetts in 1802) and provide the building stone for New York’s iconic brownstones.  

These rocks formed as the supercontinent of Pangaea disintegrated, rifted apart to leave the testaments of red sandstone separated by the Atlantic Ocean:

Therein lies a story that links the mediaeval troglodytes of Nottingham with the Battle of Gettysburg – but that’s for another day.

 

[Thanks to Geoff Manaugh at his ever-fascinating BLDGBLOG for alerting me to the story of the Nottingham cave survey. Nottingham images from the caves survey project website.]

 

Comments

[Jules]

Great story and images Michael;so many deep connections in time and places. I must be from the late Pilocene also, but my plaque, if there was one, probably rotted away in the East Texas humidity! Wonderfully detailed little fly through video on Geoff's BLDGBLOG.

[Richard Bready]

All children should grow up with nearby caves, the fastest way to learn to love the earth below. Less relevant, but irresistible, this passage from Lyttleton's Britain, the gazetteer from I'm Sorry I Haven't A Clue:
"It's well documented in official records that the city's original name was 'Snottingham' or 'home of Snotts', but when the Normans came, they couldn't pronounce the initial letter 'S', so decreed the town be called 'Nottingham' or the 'home of Notts'. It's easy to understand why this change was resisted so fiercely by the people of Scunthorpe."