Underground Greenwich (6) Diamond Terrace's Mines.

Ok, put that shovel away. Not diamond mines, I'm afraid (unless you're counting the houses themselves...) But highly interesting all the same.

Strange, isn't it. I've been trying to track down information about this for months - ever since I heard about a council worker who used to go potholing in his lunch hours in the 1960s. I tried to find him, with no success. I even tried to find the results of his excursions at the London Spelaeological Society's archives. Then, there I was looking for something completely different, when what should I find but the report of 'another' excavation I hadn't even heard of. It would seem I'd been digging in the wrong place all the time. Harry Pearman was enjoying his energetic lunch hours twenty-odd years later...

But back to the tunnel.

It's a sand mine. Now - I know that sounds a bit mad, since sand can be so easily dug out from overground sites, but apparently Greenwich's geography means that the strata over the Thanet Sand in this particular area is too thick to bash out from the top so they tunnelled underneath instead. Of course that means that the rock above could be used as a roof - no need for props. It also meant that once the entrance was lost, it was gone for good.

It was in 1905 that Greenwich Borough Council thought it might be a good idea to know where all the tunnels, caverns and holes are - if only so that they could make sure roads didn't get built over them and accidents ensue. They discovered a whole network of tunnels under Nightingale Lane (now Westgrove Lane) "complicated and lofty, cut into hard sand and extending over a considerable area," and recommended a survey in case of tunnels collapsing causing bits to be cut off and lost, only to be rediscovered if someone fell through into them (let's not even mention 2002 and the A2 at this point...)

By the time John Stone's lecture came out in 1914, it looks as though these tunnels could be wandered around, but even he admitted he didn't know the extent of them. As time passed, and more building took place over the area, the tunnels gradually became lost.

Fast-forward to 1985, when Kent Underground Research Group got permission from a property owner in Diamond Terrace to do a little excavation. The opening is a brick arch, followed by a set of brick stairs to a slope - where wooden steps once took the original miners down. The surveyors couldn't get very far - at least two major rock falls meant that the extensive 400ft tunnels that folklore describes are either exaggerations or lost forever. But what remains is still very exciting.

There are three galleries, connected by two cross-passages. They were hastily repaired during World War II for use as air raid shelters - the sand-bags are still down there, as is quite a lot of graffiti. The London Archaeologist (Summer 1987) doesn't mention what the writing says - but after Badger suggested I searched the Greenwich Industrial History Society's splendid website I can tell you it includes 'portraits' of Mussolini and Shirley Temple. The mind boggles as to what they must be doing...

The passage joining the two galleries is much rougher than the reset - it looks as though it might have been cut out after it stopped being a mine so that the owner could have a lovely grotto. If my garden history is correct, I'd make that around the rococo period - 18th Century.

Which begs the question 'When was this originally dug and what the hell did they want all that sand for?'

The problem with trying to date sand is that it's so soft - tool marks disappear and there's no original human evidence left. There is a beautifully-cut inscription of '1671' with 'a carved floral design,' but since even the WWII graffiti is beginning to melt away it's unlikely to be authentic.

On the other hand, the Greenwich glass industry (about which I know nothing - but believe me, I'm going to find out - watch this space...) was in full swing by that date. The report I'm reading can't seem to decide whether the glass was excellent quality or cheap rubbish - apparently Greenwich glass itself was pretty special, but the Thanet sand in this mine was poor. Perhaps it was used to make cheapo bottles as a sideline. GIHS suggest it could have been used for cleaning.

The report ends with a thrilling thought. That from the evidence found in the 1980s, this mine cannot be the one described in the 1905 description. The last lines make my phantasmagorical heart flutter. "This suggests that there is another, more extensive, mine somewhere in the vicinity. Research in the area is continuing."

According to GIHS website, the owner is very keen to keep the tunnel useable and holds cocktail parties there. Invites should be addressed to thegreenwichphantom@gmail.com...

BTW if you live in the area, don't panic. The thickness and stability of the rock here means it's highly unlikely you'll fall through into the mines while you're watching TV...

PS. See Parish News for details of another Underground Greenwich walk.