Another Erratic - Thunderstone

This is close to Shap and has always interested me as I've driven past. Why it's called 'Thunderstone' on the OS map I know not. It's bigger than yesterday's (about 90cm high) but made of the same granite. It has a characteristic of the erratics at Norber in the Yorkshire Dales ( in many geography texts) in that it has become 'perched' as the limestone below has weathered away since the ice age.