Rocks reveal the Wall is about more than Hadrian

After the collision of the continents of Laurentia and Avalonia, Britain became part of the Old Red Sandstone continent, which lay just south of the Equator in a hot and arid climate.

After the collision of the continents of Laurentia and Avalonia, Britain became part of the Old Red Sandstone continent, which lay just south of the Equator in a hot and arid climate.

This produced the red sandstone seen in buildings in Cumbria and the Borders.

Then for around 50 million years Britain experienced tropical seas and rainforests. In the Hadrian's Wall area, the rocks are limestone formed by the remains of sea creatures, mudstone and sandstone created from mud and sand carried by large rivers and coal seams, which are compressed ancient forests.

On the north bank of the Tipalt Burn near Thirlwall Castle on the Wall are superbly preserved fossilised corals. Fossilised ripple marks in sand formed by water currents are preserved at Black Pastures Quarry, near Chollerford, where even the casts created by burrowing worms 325 million years ago can be seen.

Fossilised tree stumps unearthed at a colliery near Wallshield are on show at Northumberland National Park's Once Brewed visitor centre on Hadrian's Wall.

The Whin Sill was formed 295 million years ago by molten rock which solidified into sheets of dolerite to form ridges and near-vertical cliffs at places like Peel Crags, Walltown Crag and Steel Rigg.

Walltown Quarry has a hard rock trail for visitors, who can see the cavities in the rock left by bubbles of trapped gas.

For long periods the only commercial source of the mineral witherite, used to make barium chemicals for use in glass, paint, cement and steel-hardening was Settlingstones Mine in Northumberland.

At its closure in 1968, it had produced 630,000 tons of witherite - about half of the world's output.

Around 2,000 years ago, the ice arrived with parts of Northumberland under sheets nearly a kilometre thick.

Sycamore Gap, one of the most photographed spots on Hadrian's Wall, was carved out by vast amounts of meltwater which broke through the dolerite rock.

Scouring by the ice also created basin-shaped hollows which later became shallow lakes such as Greenlee, Broomlee and Grindon loughs.

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