A short update on a remarkable phenomenon encountered earlier this year. You may remember the picture above from a previous post. It’s the Pitroddie Burn disappearing down a sinkhole in the Den of Pitroddie. It emerges from the ground a couple of hundred metres downstream, apparently none the worse for the experience.

I first encountered it in spring spate. So after a couple of weeks without rain in late June and early July, I thought I’d go back and see what it looked like. I parked at the Glendruid cottages (NO 210251), where a rusty gate gives access to the bottom end of the Den. (Glendruid comes from Gaelic druid, “starling”. Sorry to disappoint anyone expecting Celtic priests.)

In the spring, the track up the glen was a little overgrown, but easily passable. I had met a couple of dog-walkers, and had it tagged as a possible way up to Evelick Hill at some time in the future. But the summer weather had turned it into a riot of every thorny or stinging plant native to Scotland. There were shoulder-high nettles with stings that could penetrate my walking trousers. I felt a certain hankering for a machete. So I was a little fretful by the time I got to the point at which the Pitroddie Burn disappears underground, and even more so by the time I’d slid down the overgrown banks to take a look at it.

The area previously filled with water was now an empty circular bowl with a flow channel around the edge and a hump in the middle. The trickle of the burn simply dropped unspectacularly out of sight in a little patch of mud. Here it is after I’d cleared away a clog of dead vegetation. You can judge the small scale from the leaves:

I’d previously thought that there must have been some sort of rockfall hereabouts, but it was difficult to see where it might have come from. The rock cover also looked suspiciously uniform in scale, as if someone had pushed a huge dry-stone wall into the river. So I began to wonder if the river has actually been buried under the spoil-heap from the Pitroddie Quarry, which forms the whole north side of the Den just downstream from where the burn stages its disappearance, and just upstream from where it reappears.

When I got home, I checked the National Library of Scotland’s marvellous geo-referenced maps service.

Here’s the Ordnance Survey’s 6-inch sheet of the area from the 1843-1882 series:

The burn is clearly shown to flow continuously down the Den.

But here’s the same area, on the 6-inch sheet from 1899:

The quarry workings are hugely extended, and the burn is doing its disappearing/reappearing act just as it does today. So it looks like the underground watercourse was deliberately created by infilling, when a network of tracks was built to serve the quarry and smithy in their heyday. The tracks are now vanished, the buildings all but vanished, but the burn still flows underground.

This link should take you to a display of the area with the two maps superimposed. At the left there’s a menu, and a blue slider marked “Change transparency of overlay”. Slide it to the right to see the early view, and to the left to fade in the later view. Neat, eh?

So that was that. But on the way back I encountered a marvellous congregation of Green-Veined Whites, dancing in the sunlight like a little crowd of fairies.