The latent images seem to happen because of what I am calling "wet shadows", wherein normal undisturbed soil projects varying forms of darkness, depending on its water content.
Under photo color-manipulation, stone walls, or stone outlined artwork, converging trails/roads, up to 24 inches under soil, project a lighter image, because of the lesser concentration of water content. All over England, in everyone's backyard, I am seeing wonderful objects sub soil, not knowing if they are last weekend's rugby barbeque, or 10,000 year old antiquities.
And this process works similar over water, on statues, stone pillars, though not as precise.
Seems to me that the area surrounding the Hill has long been subject to flood and fluctuations in the water table; indeed, some might say that the Hill is a representative island surviving in a Winter Borne floodplain. You indicate that in your third paragraph that this is 'undisturbed soil" and yet this area would hardly undisturbed in my opinion. I've been on GE and cannot see the face that you can. The route of the Winterbourne is just that, and IMO not some anthropocentric fiddling with Good Ol' Mother Nature. I'd much rather stick with Michael Dames' theory of the "pregnant mother" - and I know that to be far-fetched too. Such a big head with such a little profile. Looks more likely to be a sheep track to me... Sorry.
Peace
Pilgrim
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