4/5. Rock-Hard Walls. It seems obvious to say that dry-stone walls are made of rocks, but when you stop to think about it they are wonderful visual adverts for British geology. Because wallers use the rocks they find at their feet. these intriguing features tell a lot about what made the British Isles. Dry-stone walls show the enormous changes the land has seen through time - from coral seas to volcanic explosions. For details see Monday