Boulders that have been carried by ice away from their bedrock source are known as glacial erratics. They are good markers for tracking ice flow directions, especially if they are from a distinctive, well-constrained source. Shap Granite boulders are ideal. These rounded, pinkish rocks with large feldspar crystals are scattered across the Westmorland Dales, particularly in the west close to their source south of Shap. A few granite boulders on Crosby Ravensworth Fell are very large, up to 2m across. Some clusters of erratics are associated with glacial meltwater channels. Shap Granite boulders are found across large swathes of northern England, as far afield as Cheshire and the Yorkshire coast.
Shap Granite erratics scattered along Blea Beck, west of Crosby Lodge. © E. Pickett
Shap Granite boulders can be found in the remains of prehistoric settlements and in stone circles, such as the Neolithic to middle Bronze Age Gamelands stone circle east of Orton. A few large granite erratics have the intriguing name ‘Thunder Stone’, suggesting that local people have long recognised them as ‘alien’. They lie on parish boundaries and have probably been important markers for centuries. Examples of ‘thunder stones’ are found at Trainriggs, Great Asby Scar and near Howe Nook west of Orton. Another large erratic within a wall on the slopes of Great Kinmond is known as Mitchell’s Stone.
The ‘Thunder Stone’ on Great Asby Scar, within a wall along a parish boundary. © D. Evans
The Trainriggs ‘Thunder Stone’, a dramatic Shap Granite erratic east of Shap. © E. Pickett