I'd be interested to hear what the score is down Yorkshire way with the groove/fissure thing. I think there's got to be something in it in the D&G area carvings, and reasonable evidence for it in Argyle.

It's a bit harder to claim anything in Northumberland, but I think the connection is still there, just mutated into a slightly different form, with emphasis on the local natural features on a wider scale rather than the features on the surface that actually bears the carvings. This possibly being in the absence of the cracked/fissured metamorphic surfaces found north of the Whin Sill.

I'd think that the Pennine stuff would be more like Northumberland, due to similar stone, and would hence also be very interested in hearing about how things are in Ireland.