I can't convince myself they're ploughmarks. If they were, it would seem odd that they vanish on the apex of the stone. Also, can't see any sign of the 'juddering' marks I'd normally associate with a plough being scraped with force over a stone.
The grooves do look more akin to the Welsh arrowstones than to the Fyfield polisher, but the bit below the groves on the Elva stone looks suspiciously flat/smooth.
I reckon it's possible the Fyfield jobbie gives a bit of a false impression of how glassily smooth polissoirs should be, as it's on sarsen, thus less prone to the roughening effects of the weather? What kind of stone are the french polishers on?
Btw, the link TE posted is to a page that's moved on, the original page is now to be found at:
http://www.keswick.u-net.com/80602.htm
