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Burrington Combe on a wet Thursday

Published (updated: ) in places, walking.

Burrington Combe is an atmospheric cleft in the rocks in north Somerset, about an hour’s drive from my house.

To most visitors it’s just a nice scenic bit of road, but to lo-fi geology nerds like me it’s a fabulous playground of fun.

Today, it’s green and wooded and has a not-too-busy road down the middle. But 500 million years ago (give or take a few million either side) it was a desert wadi, rather like some of the landscapes Kate and I saw when we visited Oman in the 1990s. Yes, north Somerset once looked like that.

The land immediately south of the Combe is an anticline – a hill, where the rocks have been bent upwards like a letter “n”. When they were freshly bent, they would have been a lot higher than they are now – but erosion happened, as erosion does, and the tops of the hills got washed away.

Washed away, down through the steep sided valleys and wadis on either side. Now, there is a car park and a toilet block. Then, there were rocks and gushing, whooshing water.

The topmost layer of rocks was a layer of limestone, and the thing about limestone is that it dissolves.

Consequently, you get things like caves and swallets. Swallets are the opposite of springs: they’re places where streams disappear into the ground.

And because Burrington Combe has been patiently waiting for millions of years before we came along and built a road through it, the water that once gushed through it now mostly gushes below it.

What the water leaves behind is caves: vast, complicated death-trap caves like Goatchurch Cavern. You can walk right up to the entrance, but don’t whatever you do go inside unless you (a) know what you’re doing and (b) have the right equipment.

So, staying out of the caves (because I don’t know what I’m doing, and I don’t have the right equipment), I’m more likely to follow the squishy, muddy, quite-often-actually-a-stream footpath upwards to the top: to Black Down.

From here you can look right across the top of the Combe at the layers of rock on the other side. You can picture yourself back in the wadi days, when the weather would have been blistering hot, and dinosaurs hadn’t been invented yet.

Beneath your feet the footpath is red, because Black Down is made of sandstone, the rock that was laid down underneath and before the limestone. All the limestone that used to be here, at the top, got eroded away millions of years ago. Different rocks means different vegetation: up here on the sandstone it’s all ferns.

You go up, you come down. A footpath brings you back down to Burrington village. Back in the old wadi, with the road through it.

What I love about this stuff, about clambering around in rocky places and guessing how they turned out that way, is the sense of unimaginable history. Not yer wars-and-famines, kings-and-queens history — these rocks predate people completely. This is planet-level history. Drive through this combe, and you’re driving through deep time. That’s what wet Thursdays were invented for.