Nigel Hawkes and Nick Nuttall report from the BritishAssociation for the Advancement of Science on Wonderland clues, risingseas and unseen pollution

Oh my ears and whiskers! A geologist has identified thehole in the ground that must have inspired Alice's big tumble as she pursuedthe White Rabbit.

The cause of her fall, says Tony Cooper of the BritishGeological Survey, was the soluble gypsum rock that underlies Ripon inNorth Yorkshire. At regular intervals the dissolving rock causes collapsesthat create holes large enough to swallow buildings.

Lewis Carroll, the author of Alice in Wonderland, wasbrought up near Ripon and visited the town many times. Not only must hehave been aware of the holes, Dr Cooper told the British Association meetingin Sheffield yesterday, but there is another connection.

Carroll's father had a close friend, Canon Badcock, wholived at Ure Lodge in Ripon. His daughter, Mary Badcock, was later usedby Carroll as the model for Alice's appearance. He gave a photograph ofher to John Tenniel, the artist who drew the original illustrations, withinstructions that this was how he wanted Alice to look.

In Carroll's day there were many collapses in the fieldsopposite Ure Lodge and it is likely that in 1834 he visited a dramatichole that opened up about 300 yards northeast of the house. This left ashaft more than 60ft deep and 35ft in diameter, with solid rock exposedat the sides.

"Down, down, down. Would the fall never come to an end!"Alice thought to herself as she fell. In Carroll's time, the holes wereindeed believed to be bottomless. Near the village of Croft, where Carrollgrew up, was Hells' Kettle, a huge hole filled with water. Prosaically,divers who have plumbed its murky water in recent times have found it isa mere 20ft deep, but that was unknown to Carroll.

The dissolving rock under Ripon is gypsum - chemically,calcium sulphate - originally laid down when the area was under an enclosedsea in tropical temperatures more than 250 million years ago. The evaporatingsea left behind the gypsum sheets that lie sandwiched between water-permeablelimestones.

Underground streams flow through the gypsum, said Dr Cooper,at depths of 100ft to 350ft. Over the years channels form as the gypsumdissolves. Eventually the rock is so weakened that it can no longer supportthe overlaying ground. In Carroll's day Ure Lodge was the solid home ofa clergyman. But in 1997 a huge hole appeared close to the house, destroyinga row of four garages. The house itself has now been demolished.

"The insurance company paid for that," said Dr Cooper."But it will not take responsibility for the land. So the owners are nowfacing lawsuits against them for the reinstatement of the land, where agroup of houses had been built in the garden of Ure Lodge. And as the holeis large, that is pretty difficult to do."

Fortunately, the belt of gypsum running through Riponis fairly narrow, no more than a couple of miles wide. Where gypsum occurselsewhere in Britain, the problems are less serious because the rock isusually sandwiched between mudstones, which water penetrates less easily.Along the Ripon gypsum belt, special building regulations apply to controldamage by subsidence.

Bridges on the Ripon by-pass have been specially builtso that a collapse of the ground under any of the supporting pillars willleave the bridge standing.

There are also problems abroad. Around Zaragoza, in Spain,collapses are so frequent, Dr Cooper said, that farmers crossing theirfields late at night attach long planks across their shoulders so thatif the ground opens up beneath their feet they will be left suspended.Curiouser and curiouser, as Alice remarked.