Coordinates provided by Olier62, whom I always trust : 50° 15' 56.42" N 3° 12' 42.97" E
Polissoir, found at Aubencheul-au-Bac in 1968, when the river Sensée was being widened.
Classified in 1980.
The polissoir is now (since at least 2012) protected by a glass housing.
I'll go and visit this monument one of these days.
Something is not right. This message is just to keep things from messing up down the road