Hidden away behind the clink and tinkle of the yacht masts and rigging in Sunderland Marina stands the modern facing MAC or Marine Activities Centre.

You'd be forgiven if you thought that this was just where you pay or pick up your life jacket for a spin out at sea.

Climb the steps to the reception, open a humbly glazed door, and you're in for an archaeological astoundment. Home to a fairytale phenomenon, grizzled and twisted, knotted and gnarled; this is the home of the North Dock Tufa!

Looking at it, it's hard to put into words just what this is. It looks like a prodigious pizza oven with the fringe of swinging sixties Paul McCartney. Or a stately fireplace covered in dripping candlewax.

I'd never seen anything remotely like the Tufa. So what is it? I know you'll be wondering!

Does a 'calcareous dome of calcium carbonate' help?

Nope...me neither. Let's go back to the beginning and start with a bit of history and a science lesson!

Though this isn't new to some Sunderland folk, it's a geologically significant first for Sunderland. Some people will have been aware of this for well over 150 years.

It might not have been given its distinct scientific name until the 1990s, but the people of Roker were well aware of this calcareous curiosity hiding in the harbour, some gathering water on the regular to furnish their brew or bend their creels. Some say that two old Polish men kept a still there for the illicit distilling of spirits! The story, like the Tufa swells!

The North Dock, shown here from above in this image from Tyne & Wear Archives & Museums in 1957, is now home to a thriving art trail at St. Peter's. It was designed back in 1831 by Victorian engineer Isambard Kingdom Brunel, and was funded by the Wearmouth Dock Company under the ownership of Sir Hedworth Williamson. However, the dock never amounted to much because of its small size. It was disparagingly referred to as 'Sir Hedworth's Bathtub'. How to kick a knight!

In the 1950s, much of it was filled in, and in the early 1990s, land was cleared in the North Dock harbour, where the old Sunderland Boat Club and fishing huts were demolished, making way for the shiny new Marine Activity Centre.

Now, many sailors, fishermen and allotmenteers were well aware of this seep of water, but it wasn't until demolition began that this strange, solidified dome was formally recognised and named as The North Dock Tufa (pronounced Toofaa in my Northumbrian accent. I'll spare you a Makem attempt!)

This errant trickle must have developed some time after Brunel built his beefy harbour boundary walls, as between then and the early 1990s, this calcareous flow had grown and grown, licking the leaves of the foliage that fell in its path.

Thanks to Robbie Breeds for the photos of the old harbour.

Now when I was a youngan, my mam regularly would say, if she was cornered by a spider, “Eeeee George, I was petrified”.

In literal terms, this would have meant she was turned to stone!

Here, this is just what's happened.

Over the decades, the drips of water coming from, no one's quite sure where, have carried with them elements of calcite. CaCO3 is a compound of calcium carbonate. It's made up of the same sort of ingredients that make eggshells, seashells and snail shells. This water is rich in dissolved calcite, and it coats whatever lies in its path. Look at the old lobster pot, coated and captured in time!

It's prevalent in rocks like limestone and marble, and when coupled with the constant drop, drop, drop of a steady flow of water, it covers whatever is in reach and creates petrified pieces of plant matter!

Remember old school science mnemonic: Tights fall down, and mites crawl up!

Look how the head of the Tufa is crowded with hundreds of stalactites! It's otherworldly. Mysterious and complex in its drips and drops. Years of history are held in these witchy fingers. If walls could talk, these would have some tales to tell! Layers and skins over things which once lived are now frozen in time. And the Tufa is constantly gaining, with these calcite-rich waters creating a vegetation veneer.

So significant a find was the North Dock Tufa that when geologists identified it as the most important example of a tufa in the North East, plans were rewritten for the Marine Activities Centre. Architects redesigned elements to make a feature of the Tufa.

A frame was built around it to offer support. This has now been swallowed up by the Tufa as an evolving structure. Huge amounts of concrete were poured into the base to secure it and bore holes were drilled through the harbour wall and stitch anchors fitted between the wall and the Tufa. It has to be kept in check and trimmed back so as not to become hazardously heavy. What a job being the tufa barber!

Look at the grey-green fingers emanating from the structure's ceiling. The vegetation that once created the mould for each stalactite has disintegrated over time, leaving the shape of the plant in newly formed soft rock, each one with a tiny pinprick hole at the tip of each tube. Samples were taken and stored by the university and Sunderland Museum, and in 1995 it was prodigiously awarded RIGS status (Regionally Important Geological Status), the first of its kind in the North East. It is known as the most significant and accessible example of a Tufa in the region and the public is very welcome to pop in and see it for themselves.

Here is my handy husband measuring device to give an example of the sheer vastness of this structure. This particular variety of husband strides in at around 6ft, so this gives some indication of Tufa versus husband! (to have and to hold... for better, for worse, for richer, for poorer, in sickness and in health, to love and to cherish, to be used as a regular measuring device against unusual items, until death do us part.)

It really stuck with me that some kids in the 50s and 60s referred to the Tufa as 'The Snot'.

If you visit, I hope you can see beyond the green slip and slime, and recognise it for all the weirdness and wonder it beholds!

It's genuinely one of the most unusual things I've seen, and it's a right old fascinating find in Sunderland!