Metherall Settlement

This is the inside of Hut 4 at Metherall. The grid-like pattern on the face of the stone at 60 degs of the centre of its circle echoes the face of the stone that stands near Hut 5. I wondered if this criss-cross effect was natural, or man-made. This face looks towards 240 degs, and the face of the other stone (with an even more pronounced 'grater'-like face) looks towards 262 degs.
(Compass-reading recorded just in case this is important!)
Admin - you may get this twice! First one disappeared!!