http://www.ancient-wisdom.com/russiadolmen.htmThird down photo shows a portal dolmen.
IMHO.
Those zig zags are depicting the bloch walls detectable there, and will formulate on geometry at a point within the dolmen, where the central line passing through that round hole is.
A quartz plug will have filled that hole and will have glowed as the moon reversed the flows.
Bloch walls are formed as a detectable zig zag wave pattern between opposite spin magnetic lines ( opposite polarisation)
Kevin