Even in the spring sunshine this quarry gives me the creeps. A huge hole in the ground, its hacked-out walls still bare and dripping a hundred years on.

The sun is hot on my back for the first time this year; I feel overdressed in my winter gear. A peacock butterfly flits away from my casting shadow as I follow the rough path down to the bottom. A faint whiff of coconut from the flowering gorse is a comfort. With frightening suddenness a military jet roars low overhead and the noise, amplified in the bowl of the quarry, has me cowering and covering my ears.

Under a dripping overhang the height of a parish church, a five-foot high, black-mouthed tunnel disappears into the hillside – God knows where too. I try to imagine dragging slate out of that forbidding hole day after day. Somebody has been burning plastic rubbish near the entrance. The quarrymen wouldn’t have known what plastic was. A wren belting out his song from a sallow bush is pumped up to Pavarotti volume in here – which no doubt pleases him.

Amongst the bushes is a shallow pool that has all the charm of a large puddle on a construction site. Graffiti scratched by bored teenagers or besotted lovers decorates the slate blocks littered around it. The bottom of the pool is strewn with slate debris covered in algal slime. Nothing else grows there. Several pale brown newts wriggle away to hide under stones, as if shunning the light. I am puzzled by four perfectly synchronised brown marks twitching across the underwater rubble. Eventually it dawns on me that they are the shadows of depressions in the water’s surface made by a pond skater’s feet. These insects truly can walk on water.

In the water on the far side of the pool I find what brought me here: toads, dozens of them. Some are scrabbling for an amorous grip on overwhelmed females. Others are hanging motionless in the water, as if caught in amber for a thousand years. They seem oblivious of my presence. Lines of spawn criss-cross amongst them, like tape spelling out their DNA code. There are dead and half-dead ones drifting amongst them. Why do they come back to this God forsaken place each year to spawn? Yet somehow they match the quarry in their cold-bloodedness; mindless and blind to everything except reproduction in this hole in the ground. It is like some post-apocalyptic glimpse of what life might look like after we have gone.