Inspiring underground secrets of kamenitza and grikes

In medieval times, pilgrims to St Patrick's Purgatory on Lough Derg, Co Donegal, spent a day and a night alone in a penitential cave on the island, hoping for visions. Before the entrance was blocked in the 1600s on peremptory orders from Dublin, even a Papal Nuncio, Chiericati, had sought the kind of exaltation that might flow from long immersion in silence and darkness.

Today, Ireland's real rock caves invite a whole new range of seekers after knowledge and adventure, and pilgrims to some holy wells are still drawn to the archaic mystery of caves as sacred and awesome places.

Marion O'Dowd, an archaeologist at UCC, writing in the current Archaeology Ireland, talks of myths that featured caves as the sinister haunts of wicked hags - a black-propaganda spin, perhaps, born of the oppression of pagan religions by a patriarchal Christianity (all the saints associated with Irish caves today, she notes, are men).

Her professional interest, however, relates more to what myths suggest about Ireland's caves as places of prehistoric burial and ritual. Their importance has been underestimated, she argues, because most of the known caves were excavated in the 19th and early 20th centuries by palaeontologists, whose main interest was sub-fossil animal bones. Compared with a mammoth's hind leg or a hyena's jaw, the odd human femur, axehead or amber bead were gathered only as an aside.

Most of the artefacts collected from caves date from Early Christian use. But the yield of Neolithic and Bronze Age burials and grave goods has been promising enough to keep archaeologists sifting away by lamplight. Dr Peter Woodman of UCC is even hopeful that areas such as east Waterford might yield human bones from the Pleistocene epoch - wanderers from the Britain of more than 25,000 years ago.

New caves with new deposits are the archaeologists' dream (might there be, on the wall of some unsuspected limestone cavern, even one half-way-decent doodle of a giant Irish elk?). The wider realisation that large slabs of Ireland are as full of holes as GruyΦre cheese may raise such improbable hopes, but also the desire of geologists and speleologists to share the wonders of the underworld with people who know only two dimensions of the Earth.

ALMOST all the island's caves, from the Marble Arch system in the Cuilcagh mountains in the north to the caves of Clare and Munster, were carved out through the solution of limestone by water in the process known as karstification. Earlier this year, the expert Working Group on Karst, based in the Geological Survey, published a popular booklet about the landscapes, caves and groundwater systems of karst and the concern for their conservation.

Now one of the group, Trinity College's Dr David Drew, has produced a booklet on the Burren karst for the Classic Landform Guides published by the UK's Geographical Association. This is a landscape Dr Drew has made very much his own, delving into cave systems alive with the sound of rushing water as well as the intricate surface sculpture of clints, grikes, turloughs and sinking streams.

Readers of his booklet will learn a few new words relatively painlessly (kamenitza is one I like - the egg-cup hollows that standing water makes in limestone). It also makes fascinating sense of the Burren's often surreal landforms, and of the routes to take through some very confusing topography.

This is state-of-the-art knowledge: uranium series dating of cave calcite deposits, suggests, for example, that while the Burren's simple stream-passage caves have been formed since the last ice age, the more complex ones may originate from at least the last interglacial era, 120,000 to 132,000 years ago.

Dr Drew limits his caves to two examples: the young, stream cave Polldubh on the western flank of Slieve Elva, and the visitors' show cave, Aillwee, above Ballyvaughan, whose main passages may date to more than 350,000 years.

What, I wonder, would be the age of Pol-an-Ionain, the great cave near Lisdoonvarna at the centre of which hangs a spectacular stalactite 6.5 metres in length - perhaps, if one trusts the Guinness Book of Records, the longest free-hanging specimen found anywhere in the world?

The main cave, itself a marvel at 40 metres long, is reached by 550 metres of low crawling passages (a "knee-wrecking" journey, as cavers have put it). They are entered at the foot of an ivy-covered cliff-face - hence the cave's name - on the farm of John and Helen Browne.

The cave was first explored by potholers in 1952. Helen Browne made her first crawl to see the stalactite some 20 years ago and for a decade she and her husband have nurtured a project to make Pol-an-Ionain a show-cave, with a karst interpretive centre, comparable to that at Aillwee. But a proposal to use explosives in carving out an alternative entrance has raised concern about the effect of vibration on the stalactite.

Appeals to An Bord Pleanβla against planning permission granted by Clare County Council have led to a requirement for an environmental impact survey. Among its technical needs would be an X-ray of the stalactite, the mechanical logistics of which, on the face of it, present insuperable difficulty. Forced back to the drawing-board, the resilient Helen Browne is exploring the options for silent tunnelling.

Among persistent objectors to her project have been the Speleological Union of Ireland, a body actively concerned with conservation and proper conduct underground. But Helen Browne describes how, over the years, what one pictures as a sparkling Sword of Damocles has been spattered with mud, clearly scooped up from the floor of the cave and thrown against the tip, some three metres up. A caver friend, confirming this, finds it incredible that anyone who has troubled to make the punishing crawl should then be overcome by such an impulse.

Classic Landforms of the Burren Karst is published at £8.95 in UK by the Geographical Association, 160, Solly Street, Sheffield S1 4BF, UK (E-mail: ga@geography.org.uk).