"Chisels don't make that kind of an impression. A chiselled notch has V-sectioned walls - these scars have parallel sides"

Blunt chisel, on the side, used to crush, rather than cut?

PS. Imagine a continuous row from Shap, across Kirkston pass, then following the Maiden way, across Simonburn, snaking up past the Five Kings then on to the Shearers. With a cupmark on every stone ;)