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Looking at the Swindon Stone that Christ Church is built with you are actually looking at a fossilised Jurassic Sea Bed.

A Fossilised Jurassic Seabed

And if you look closer you can actually spot bits of seashell and sand.

But shells and sand aside Swindon Stone is actually made up of material that has literally gone through a fish's stomach. We're talking fish pooh here.

In the warm sub-tropical Jurassic seas, that covered Swindon, fish fed on a high roughage diet of corals and molluscs. Crunched up and digested they passed through the fish's gut and emerged as ground up bits of calcium carbonate.

And it's still happening today. If you look at a lovely coral beach in the Maldives, for instance, you are basically looking at a pile of fish pooh.

Close up of Limestone

Meanwhile back in Swindon the Jurassic Sea was not only warm and sub-tropical, 28-29 degrees, but very shallow, maybe 10-15 metres deep. And with all that fish pooh around it was becoming supersaturated with Calcium Carbonate.

Like a kettle annoyingly deposits limescale all over its element Swindon's Jurassic sea was primed and ready to precipitate massive quantities of Calcium Carbonate all over the place.

All it needed was a change in temperature, for instance, to trigger a change in chemical conditions on the seabed and calcium carbonate would be instantly precipitated.

And when conditions were right everything got coated in calcium carbonate including tiny little grains of sand or shell known as oolites.

If you look closer at the Swindon Stone you can actually see the tiny little pits or oolites. And they still form today in tropical seas but only in tropical seas.

On the corners and around the windows at Christ Church you can see the smoother Bath Stone, which is almost 10 million years older than the Swindon Stone.

...leave Christ Church and turn left on Cricklade Street and head towards the High Street