It is not as widely known as it should be that Britain has the most varied geology of any country in the world. This book is a celebration in words and pictures of what its mountains are made of, and how they got there. This in turn determines what they're like to climb, scramble on, or walk over. Why is Skiddaw slate so slippery? How do tors form? Why is gritstone so difficult? Why is Lakeland so picturesque, and the granite lands so grim and forbidding?



Geology is destiny, whether it's the rubbishy nature of gullies and screes, the sculpting of valleys by ice or the landslip weirdness of Quiraing on the Isle of Skye. British mountains contain many interesting and different ingredients: gneiss and granite and gabbro; limestone and sandstone; schist and slate; the product and the debris of tectonic shifts, volcanoes, earthquakes and glaciers over many millennia.



This book explains all this to the layman, from an expert but personal perspective, and will add immeasurably to the fun and satisfaction to be gained from any day in the hills.

Contents



1. The Crunch of Continents

- Various earth-shattering events of the last two billion years: Scotland crashes into England; the UK drifts north through tropics; the nudge from Africa; the opening of the Atlantic.



2. The Work of Ice

- Glaciers carved the shapes as we see them today



3. Gneiss Times

- The Lewisian Gneiss, in the Outer Hebrides and Wester Ross; landscape of knock and lochan; a moment in the Malverns



4. The Monsters of Torridon

- Sandstone lands of Wester Ross; buried landscapes; the origin of our oxygen



5. Quartz and Quartzite

- Beinn Eighe and the Grey Corries; the Moine Thrust



6. Squashed Stones: Slate to Schist

- Metamorphism, rocks cooked and crushed; shale to slate to schist; the Mountains of Moine and the Dalradian schist



7. Greywacke and the Ruggednessof Rhinog

- How ocean-bottom sludge became the rock of the Rhinogs



8. Shales and Underwater Mud

- More ocean sludge in the Howgills, Isle of Man, mid-Wales and the Southern Uplands; the life and times of the graptolite; Charles Lapworth in Dobbs Linn



9. All-Terrain Lakeland

- Volcanoes and slate, grey shale and granite; four different sorts of country but only one Lakeland



10. Red-Hot Flying Avalanche: Ignimbrites in Snowdonia

- Various cataclysms above Llyn Idwal



11. Walking the Fault

Faults, and a walk along one in particularm the Rossett Gill Fault of Lakeland



12. Andesite and Rhyolite

- More volcanoes, at Ben Nevis and Glen Coe; collapsing cauldrons



13. Granite Lands

- Cairngorms, Dartmoor, Arran, Mourne, Galloway - very different but all of them a bit grim; the cause of tors



14. Stone Arriving Sideways: Dolerite Intrusions

- The Whin Sill in the north Pennines, Arthur's Seat in Edinburgh and God vs Mr James Hutton



15. The Sands of Time

- The Old Red Sandstone of the Brecon Beacons; the New Red Sandstone fails to make mountains



16. Mountain Limstone, Millstone Grit

- Yorkshire and the Peak District; lime to grit to shale: the Yoredale Series



17. The Black Magic of Gabbro

- The Tertiary Volcanic Province; the Black Cuillin of Skye



18. Basalt Lands and the Opening of the Atlantic

- The Death of Gaia; Lakeland Lavas, black rocks of Snowdonia, and the Quiraing on Skye; a round-up of the red-hot rocks



19. A Two Hundred Million Year Walk Over Dufton Pike

- Brekaing the Law of Superposition behind Dufton Pike, with a visit to the Great Whin Sill



Conclusion

- My country, your country, further reading and more things to see



Reading about Rocks

Glossary

Index

Index of Places

Acknowledgements

Chapter 7 - Greywacke and the Ruggedness of Rhinog



Greywacke is the harshest of rocks, rounded, rough and gloomy grey. Its looks reflect its origin, as it forms from underwater mud at the bottoms of deep ocean trenches.

Greywacke counts as a sort of sandstone, composed of an assorted mixture of coarse and fine grains. However, deep oceans have no oxygen. So greywacke shows no cheerful rusty-red or orange colour, but a dark deep-ocean grey. Its inidividual grains are sharp-edged, as there's no desert wind or brisk freshwater current to rub the grains together, just the slow stirring of the mud currents. To get the very toughest sort of concrete, builders mix sharpsand together with an aggregate of both fine and coarse particles. Nature has done the same in making greywacke. Greywacke doesn't separate into handy slabs, nor does it welcome the carver's chisel. The stonewaller of the Southern Uplands, who has to deal with the stuff daily, develops a sore elbow and a short temper as well.

Here's how sandstone ought to happen. A large river delta slides into the sea. The pebbles and gravel drop out at once, but the sand is carried on out to sea before sinking to the bottom; the silt and mud are carried even further. And so, a few kilometres offshore, sand falls, and keeps on falling for some thousands of years until an earthquake diverts the river, or the seabed rises. Thus, eventually, one bed of ordinary sandy sandstone; and, further offshore, a bed of silty mud.

Greywacke isn't like that at all; so it presented a bit of a mystery. Its bed are a promiscuous mix of sand, gravel, grit and silt. They are also, in places, unduly thick: a single bed may be metres deep, with no internal bedding structure at all. Desert sand is yellow or orange, as the New Red Sandstone. Sand recently carried out to sea can be more brownish, as the Old Red Sandstone and the Torridonian.

Rocks are formed by processes visible around us today. But the process that forms the greywacke is different and was, until 1929, completely unseen. And the greywacke, though technically just another sort of sandstone, makes a different sort of mountain altogether. That different sort of mountain is the Rhinogs.