Now this is weird

I’ve seen some pretty weird things on blip, but nothing like this.

About 10 years ago we had a willow tree taken down. It had been planted by the original owners and had grown far too large. The tree fellers weren't able to grub up the stump because the tree was too close to a wall and it was impossible to get a machine close enough. So they cut it level with the ground, gave the stump a liberal dose of something quite nasty and left it in peace.

We put some weed-proof membrane over the area and covered it with gravel. And that was that; or so we thought.

In the spring we noticed that a couple of crows had been digging in that spot and it turns out they were after the weed-proof membrane as some sort of trendy nesting material. This morning I cleared away the gravel to re-lay the membrane and found this. I say ‘this’ in the singular; there are in fact three of them. This is the largest. It’s about 6” across and sits smack in the centre of the old stump. The other two are just a few inches in size and appear to be growing(?) out of the edge of the stump.

I assume it’s some sort of fungus - but it has ‘absorbed’ the gravel - and is rock hard. A living stone?

It’s like something out of Dr Who, but I’m sure there’s a more rationale explanation. If anyone has any idea as to what this is, I’d welcome their thoughts.