Twixt Austwick and Clapham in Crummackdale lies a group of erratic boulders called the ‘Norber Boulders’. (No grafitti unlike this in USA)

Erratics are large rocks deposited by glacier or ice flows on top of the natural underlying rock strata.
Norber boulders are dark grey green Silurian slates and sandstone grits. They were originally carried up from the fooor of the valley by glacier moving south from Ribblesdale. They were left stranded on top of the lime stone.
Unprotected limestone has eroded by rainfall and the boulders often stand on limestone pedestals polished and scratched by ice.

A great walk with accompanying photographs is available on the walking englishman
See also what to see in Clapham

Yeager Rock above is a large glacial erratic on the Waterville Plateau in Washington USA. Erratic was one of many dropped by the Okanagon lobe of the last glacial period.

Erratic Rock State Natural Site by Frederick Miller et al plus ‘Big Rock Glacial Erratics’ by the same team are the geology books of choice on the subject of ‘Erratics’.