Greetings Jacksprat,
I think the meaning of "standing stone" is given to a stone that has been stood up by human means, because it can't stand in the desired position for long without securing it in a pit. Standing stones are (mostly?) stones that would not normally stand unless placed in a man-made pit, usually of a particular long, not round, shape, and usually positioned on end.
The Thunder stone is obviuosly not of the shape suited to standing stones. Why waste the energy of digging a pit for it when it won't be going very far due to gravity, the elements, or human interaction?
Passing over Shap on the M6 one (at least one who is interested in prehistory) can interpret the many "erratic" boulders to be part of circles and avenues, which is most distracting and frustrating, as there is nowhere legal to park.
Perhaps the Shap Avenue incorporated many natural stones in their original positions, and as such not recognised, or maybe huge erratics were simple moved a few hundred yards into place, without the need for holes. A very economic state of affairs if you ask me.
It's an interesting thought you've started.
Cheers,
TE.
