Jackson, Ian. Northumberland Rocks — 50 extraordinary rocky places that tell the story of the Northumberland landscape. Newcastle upon Tyne : Northern Heritage, 2021.
The richly illustrated and accessible book series of Northumberland, Cumbria and Durham Rocks are available to purchase from Northern Heritage.
Theme: Volcanoes and molten rock
Immediately north of the B3618 Military Road
Limestone Corner is not limestone, it’s Whin Sill dolerite. This is part of the ditch that the Romans dug immediately north of Hadrian’s Wall. Here they did not succeed, the hard igneous rock defeated them.
You can see their attempt to create the ditch; broken boulders are scattered around and in one large block you can see the chisel marks the Romans made to try and split it. Curiously their colleagues digging the Vallum (the behind-the-Wall ditch), in the same rock about 100 metres further south, managed to finish their job. The Wall and the ditches were constructed between 122 and 128 AD.
The Whin Sill is an igneous rock. 295 million years ago it was molten and injected into the surrounding Carboniferous sandstones, limestones and shales.
As you walk along the base of the quarried ditch look out for wild thyme and wood sage growing in cracks and on the shelves amongst the rocks. The dandelion-like flowers of mouse-ear hawkweed are also common here. At the eastern end of the channel see if you can find the tufts of parsley fern, uncommon in Northumberland, growing in shady crevices.