0:00:31 > 0:00:32Three bounces.
0:00:32 > 0:00:33Irresistible, isn't it?
0:00:33 > 0:00:36You just know that early man stood on beaches like this,
0:00:36 > 0:00:38trying to see how many times
0:00:38 > 0:00:42he could make a flat stone bounce on water.
0:00:42 > 0:00:47The world record was set in 1992 with an amazing 38 bounces.
0:00:48 > 0:00:52Believe it or not, someone has actually worked out
0:00:52 > 0:00:55the optimum angle for a flat stone to hit the water,
0:00:55 > 0:00:58if it's going to get the maximum number of bounces.
0:00:58 > 0:01:00That angle is 20 degrees.
0:01:02 > 0:01:06But the real star of the show isn't the person skimming the stone,
0:01:06 > 0:01:08but the stone itself. The pebble.
0:01:11 > 0:01:14To help me find out where beach pebbles come from,
0:01:14 > 0:01:18I've met up with Twm Elias from the Snowdonia National Park
0:01:18 > 0:01:21and Professor Cynthia Burek of Chester University.
0:01:21 > 0:01:25It looks like a gigantic mud pie, Cynthia, but geologically,
0:01:25 > 0:01:26what is this?
0:01:26 > 0:01:30This is a glacial till, formed in very different conditions
0:01:30 > 0:01:32to those we have today.
0:01:32 > 0:01:35This formed about 17,000 years ago,
0:01:35 > 0:01:38in the last Ice Age when the area was covered
0:01:38 > 0:01:43by half a mile or a mile of ice, and as these pebbles all moved along on
0:01:43 > 0:01:49and in the ice, they all ground up against each other and bits fell off.
0:01:49 > 0:01:53And they are the bits that form the components of the till,
0:01:53 > 0:01:57this so-called mud and then it dropped it
0:01:57 > 0:02:02and the ice moved over the top, compacting this
0:02:02 > 0:02:04and making it so hard.
0:02:04 > 0:02:08And it's quite exotic looking, with the variety of pebbles in it.
0:02:08 > 0:02:11It reminds me of a sultana pudding
0:02:11 > 0:02:13with bits of raisins and currants in it.
0:02:13 > 0:02:18What's fascinating is the variety of the sultanas and raisins in here.
0:02:18 > 0:02:22Some are round, some are angular, different colours and so on.
0:02:22 > 0:02:24- Such an amazing concoction.- Yes.
0:02:24 > 0:02:28Some are pre-formed pebbles, because they're already rounded.
0:02:28 > 0:02:30And some are pebbles waiting to be made.
0:02:30 > 0:02:35- So we can go from glacial debris to beach pebble over night.- Absolutely.
0:02:35 > 0:02:38Especially in the winter when you get the big storm waves
0:02:38 > 0:02:41actually pounding against this cliff
0:02:41 > 0:02:43and the pebbles falling out onto the beach.
0:02:43 > 0:02:46That's tomorrow's beach pebble.
0:02:46 > 0:02:49To see tomorrow's pebbles today,
0:02:49 > 0:02:53Twm's been on a journey along the North Wales coast,
0:02:53 > 0:02:58starting up on Anglesea where glacial mud, or till, has already eroded
0:02:58 > 0:03:02to reveal huge quantities of pebbles, each with its own story.
0:03:02 > 0:03:04OK, Twm, show and tell!
0:03:04 > 0:03:07Hold on, I have one in me pocket, and here we have a basalt
0:03:07 > 0:03:10which has come from Northern Ireland, Giant's Causeway,
0:03:10 > 0:03:12that particular area.
0:03:12 > 0:03:13And it's very distinctive.
0:03:13 > 0:03:17It's a lovely black stone, especially when it's wet like that.
0:03:17 > 0:03:21- We also have a flint. - Very toffee-coloured, isn't it?
0:03:21 > 0:03:24Yes indeed. And that probably came from the seabed
0:03:24 > 0:03:26between Ireland and the Isle of Man.
0:03:26 > 0:03:29And this bit of pink granite here, where's that from?
0:03:29 > 0:03:33Oh, yeah, that looks very much like the type of granite
0:03:33 > 0:03:34you'd get in Ailsa Craig.
0:03:34 > 0:03:38- The small island off south-west Scotland?- Indeed.
0:03:47 > 0:03:49Listen to this one.
0:03:49 > 0:03:51PEBBLES CHIME AS THEY COLLIDE
0:03:51 > 0:03:54- That's a metallic ring, almost, isn't it?- Yeah, it's like a bell.
0:03:54 > 0:04:00This is an ancient mud stone from Penmaenmawr to the east of Anglesea,
0:04:00 > 0:04:05and this actually came from the big quarrying areas above the beach.
0:04:05 > 0:04:10This was used by people in the Stone Age period for making stone axes.
0:04:10 > 0:04:13But more recently, in the 19th century,
0:04:13 > 0:04:16you got the granite quarries there as well.
0:04:16 > 0:04:18- This is a lovely smooth bit of granite.- Yes indeed.
0:04:18 > 0:04:22These were used for making the cobbles you find on the streets,
0:04:22 > 0:04:25like Coronation Street, for a start.
0:04:25 > 0:04:27- So these are local pebbles? - Indeed they are.
0:04:27 > 0:04:31And they've come down onto the beach and now they are being subjected
0:04:31 > 0:04:34to the same processes that's going on everywhere.
0:04:34 > 0:04:36You'd never think a single coast could produce
0:04:36 > 0:04:39such an incredible diversity of pebble.
0:04:39 > 0:04:43- That's the wonder of it. - I want to find another piece of that lovely black basalt.
0:04:43 > 0:04:46It's my favourite. What's your favourite pebble?
0:04:46 > 0:04:47My favourite pebble? Oh...
0:04:47 > 0:04:52- It's like trying to choose between your own children! - THEY LAUGH
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