The rocks of Fountains

Every year tens of thousands of people visit Fountains Abbey and the Studley Royal estate in North Yorkshire. What few of them realise is that beneath the magnificent ruins, the water gardens and the parks lies evidence of one of the most dramatic stories in English geology.

When the first monks came to the site it was a wild and inhospitable place. Where the Abbey now stands the River Skell meandered through its boggy valley.

One of their first tasks was to control the river, confining it within stone-lined banks. Some of the monastic buildings were erected right over the river. The pillars and vaults which supported them can still be seen today.

A great advantage of the site was that building stone was readily available. The quarries in the northern side of the valley, near the great tower, are easily visible. The rock is a sandstone, rather coarse with occasional layers of small pebbles, and those familiar with Yorkshire geology will immediately recognise it as Millstone Grit. An unusual feature of the rock is a red staining. This is variable in intensity, so that parts of the quarry face show the green-grey colouration typical of the Millstone Grit succession, while other parts are pink, brown, purple or red.

Three hundred million years ago the land surface was at about the level of the top of the Abbey tower. But Yorkshire then had no green hills and watery dales. The land was barren, a sandy desert blasted by a tropical sun. The rock for a hundred feet or so beneath the surface was affected by the extreme conditions, and iron minerals became oxidised to give the red colours visible today.

Millions of years later, during the Permian period, the country east of the Pennines lay under a shallow sea, and in its placid waters a thick deposit of limestone was formed. This is the Magnesian Limestone. It is well exposed in the Valley of the Seven Bridges, just downstream from the water gardens.

Depending on the state of the vegetation, the visitor may be able to see, in the slopes above the lakes of the water gardens, the contact between these two rock types.

A worn and weathered Millstone Grit surface represents the Permian sea bed. Above it are a few feet of gray shale, and then the basal beds of the Magnesian Limestone. The gap, or unconformity, between the two types of rock represents an interval of a hundred million years. During these missing ages the Coal Measures - so thick and economically important only a few miles to the south - were laid down and then worn away as North Yorkshire was folded upwards. West Yorkshire, on the other hand, subsided, allowing its coal seams to be preserved under more sediments.

So next time you visit England's finest ruin spare a thought for the rocks it's made of, and for the story they tell.