This is the very unusual Ratchet formation below Barbury castle, which appeared in barley on 08 06 01.  Charley Mallet estimates its 300 feet in diameter, but I think it's more.  Everybody is  remarking how it echoes and extends the ratchet which was on the great Barbury Castle Triangle formation in  1991.  There is a dirt footpath cutting across one side of the circle, but I've removed it with PhotoShop.  The crop in the central circle is laid down like a pinwheel which turns as you fly around it.