Losing Time in Vallis Vale
Visit De la Beche's unconformity, where hundreds of millions of years vanish in a single line, reminding us that Earth changes slowly—until it doesn’t
Just a short walk from our home in Frome, Somerset, accross the fields and down into the wooded hollows of Vallis Vale, lies something extraordinary—a window into hundreds of millions of years of Earth’s history. At the confluence of two babbling streams, a long-abandoned quarry face exposes two distinct layers of rock. At the bottom is a shelf of carboniferous limestone, grey and tilted, like stacks of ancient books fallen sideways. Above are horizontal bands of jurassic limestone; a golden yellow, more fractured rock that fades into the subsoil.
The line where these two layers meet has a geological term, it is an unconformity. And this is the De la Beche unconformity, named after the man who discovered it. Henry De la Beche was one of Britain’s earliest geologists and the first director of the British Geological Survey.
Uncomformities are like pages missing from Earth's history book, showing that there was a gap in time between the formation of the two layers.
Imagine you're building a big LEGO tower. You make a nice bottom layer, but then you stop playing for a long time. Over 175 million winters, the elements take their tole on your LEGO, it erodes and breaks down, bits of it wash away. Then one day, you come back and start building a new tower on top—but it's at a different angle and made of different blocks.
The De la Beche unconformity is a bit like that, but with rocks instead of LEGO, and it tells a story about Earth’s past.
The Geo Saga of Vallis Vale
🌊 Chapter 1: Ancient Sea (about 350 million years ago)
A warm shallow sea once covered the land. Over time, layers of limestone built up from shells and skeletons of sea creatures. These formed the Carboniferous Limestone you see at the bottom of the unconformity.
🏔️ Chapter 2: Mountains Rise and Rocks Tilt
Much later, huge tectonic forces pushed and squashed the land, tilting and folding the limestone. These forces may have created mountains. This was part of a massive geological event called the Variscan Orogeny.
🌧️ Chapter 3: Erosion
After the rocks were pushed up, the land was exposed to the air for millions of years. Rain, rivers, and wind slowly wore it down. This time left no new rock behind—just a gap in the record. That’s the "missing pages" in the story.
🦕 Chapter 4: New Sea, New Life (about 170 million years ago)
Much later, the sea returned. Sand, mud, and shells settled again, forming Jurassic rocks like the Inferior Oolite. These younger rocks were laid flat on top of the tilted limestone.
🧱 Chapter 5: Anthropocene
Now we can see both sets of rocks side by side—tilted ancient rocks below, flat younger ones above. The line where they meet is the unconformity. It shows us that there’s a huge gap in time, a period where something happened—but nothing was preserved—before the story continued.
The De la Beche unconformity is a silent witness to Earth's deep history—millions of years written in stone, with whole chapters torn out by time.
Today, we live in a rare moment: the last 10,000 years have given us a stable climate, the calm in which farming, cities, and all human civilisation have grown. But that period of grace, known to geologists as the holocene, is coming to an end. Some argue that we have already entered a new geological epoch, the anthropocene, where humans are the dominant driver of change at the planetary level.
Here, the pace of change is speeding up—occuring not over geological time, but in our own lifetimes. A walk to Vallis Vale reminds us how powerful Earth’s changes can be—and how important it is that we pay attention.