Polished by the lick of the tide

IN a narrow street off the seafront in Brighton, the town where I was a child, was a shop with tall, curving windows and the most ravishing display of . . . lapidary craft, I suppose you would call it. But that hardly conjures the glowing beauty of things carved and polished from onyx, jasper, agate, chalcedony, citrine, carnelian, amethyst - such romance, even in the names!

Brighton was where the Victorian craze for pebble-collecting and polishing began - first of flints, sawn open to show their fossil sponges and corals, and then of the colourful, semi-precious stones that lurked among the shingle. By the time I came along to linger at the window, the local lapidaries had long exhausted native beaches and were buying their agate in slabs, from Brazil.

Fast-forward 30 years, to the brave early days of the Kilkenny Design Centre, where a Finnish jeweller showed me pendants made from polished, oval pebbles he had picked up on the beaches of Ireland's south-east coast. Nothing flash, of course, being Finnish, but chaste and satisfying shapes in softly-banded, earthy colours, or bird's-egg speckles.

Small wonder, then, that among the gear I brought west to Thallabawn for creative contingencies were several bags of grits for polishing stones in a barrel. The theory is that you rig up a barrel, with fins on it, and let a stream go on spinning it noisily, day after day for weeks, until the grits have done their lustrous work. I still mean to try it, in an eccentric old age.

Those beaches in the south-east sound rather special. Here's Michael Fewer, walking for his book By Cliff And Shore in Co Waterford and descending to the sea just west of Kilfarrasy Island: "The beach was made up of the most magnificently polished and rounded pebbles of quartz, jasper, sandstone, limestone and flint, deposited along the shore in colourful graded banks. I am sure the unfrequented nature of the beach was the reason why particularly beautiful examples were so thick on the ground; I found it impossible to resist collecting some fine jaspers which weighed down my pockets for the rest of the day."

His beach was beside a cliff of boulder clay - the mix of rocks, stones and silt dragged along under the Ice Age glaciers and left behind when the ice melted. This soft glacial till is typical of a lot of the south-eastern coast, and its scouring in storms tumbles masses of rock-fragments, in great variety, into the tide. Some of them could be well-travelled, swept along as the ice pushed down the Irish Sea from the north.

Michael Fewer's flints, for example, do not belong to local Waterford bedrock, wonderfully varied as this is, but to the chalk strata that were stripped from most of Ireland. A geologist might guess that they had started out in Antrim, where flint-studded chalk is trapped below basalt in the cliffs. His jaspers are a kind of opaque quartz, dyed a sumptuous red by salts of iron. This could have been torn from a vein in the igneous granite of the Mournes or Wicklows.

Glacial till covers most of the coasts of Ireland, especially those in the east. But even in the west the pebbles of an open beach at the foot of a high cliff of bedrock are well mixed with stones rolling along from bays fringed with glacial debris or with drumlin islands made of the same stuff. The Atlantic longshore drift is mainly northwards, and up near Bloody Foreland the stones have been piled into massive storm beaches rising more than six metres above high water mark.

The bigger the pebbles, the more push the waves can exert, so the real ostrich eggs end up right at the top. Whole banks of these monster ovoids, often crusted with lime and bleached grey with age, build up at the more exposed beaches of Connacht. Teetering across them brings little satisfaction to the average pebble-fancier. What one wants is an easy trudge beside the breakers, picking up eye-catching, palm-sized specimens that light up at a lick of the tongue and might or might not be worth pocketing.

My own pleasure is mostly aesthetic: pebble as beautiful object. But certain crude geological probabilities are also beginning to impress themselves. Pebbles are shaped from fragments of rock rolled up and down in the swash of breaking waves. How they wear, their weight and texture, can say a lot about the classes of rock they're made of.

The heaviest round or egg-shaped pebbles are likely to be igneous rock, especially when speckled with crystals, such as granite or gabbro. Sedimentary rocks, such as limestone, can make pebbles of quite weird shapes, especially when banded with tougher materials, like quartz. The softer sandstones, shales and slates usually end up as the flattened ovals one "skimmed" with as a child.

The third kind are metamorphic pebbles - ancient rock changed by heat or pressure. Gneiss, mostly ovoid, looks like a banded sort of granite; schist is the flaky, slightly glittery, flattened ovoid; marble is so tough and crystalline throughout that any amount of rolling and rubbing in the waves leaves it more or less round.

OTHER stone gives itself away by feel. Serpentine, usually a lovely jade green, feels waxy without really being soft. Soapstone is a heavy, grey- green rock but one of the softest, grinding down to talc: I carved a passable bull from a hefty pebble of soapstone looted from the shore on lnishbofin.

The very hard, semi-precious stones - agates, carnelians and the rest - are of cryptocrystalline quartz, translucent and glowing with colour (from mineral impurities - who cares?). There are many agates, it is said, in Old Red Sandstone, quarried in huge slabs by the waves at the ends of headlands in Kerry and Cork. There is amethyst among the quartzites of Achill Island, and aquamarine in the granite of the Mournes.

What you do is pick a strip of small shingle, still wet from the tide, and walk very slowly along it, your hands clasped behind your back. The sun, of course, has to be dead ahead of you, to light up, the little glow in the one stone in a million.