Careful there fella don't get excited. Just because the chalk is porous, it doesn't hold that it's comparable with the ceramics used as food vessels. The existing techniques for chemically analysing ancient food residue are looking at the bits of prepared food that's been protected by burial. I get the impression that the right conditions for this kind of opportunity are quite rare. I wouldn't stake a whole packet of biscuits on it, but I'd think that dryness is probably very important, so that the remains of the food couldn't be got at by the usual microbes involved in decomposition.
The fact that chalk is porous isn't the same as it being a suitable ceramic matrix for the preservation of ancient biomolecules. The chalk has been washed by thousands of years of rain.
Then there's the issue of whether wheat residues are soluble in the first place. From what I've seen of flour, it doesn't dissolve. I'm sure there's probably some stuff in wheat that does dissolve, but it'd be in such small quantities that it would be easily washed away by the rain.
Which does still leave the chance that if there had been a lot flour lying over the soil, some bio-stuff, bits may have dissolved and been washed down into the cracks in the upper layers of the chalk, where it's a bit fractured by weathering, in which case you'd probably be better off looking for an increase in the background level of things that are more likely to dissolve, or at least go very colloidal. Maybe starch? I dunno.
Thing is, (again) that even if this had happened, by now, those biomolecules would have long ago been food for bacteria.
More importantly, from a sciencey point of view, what you could do would be reverse the train of thought. Instead of looking for evidence to support your hypothesis, try and think of something that you could test for, which if found positive, would invalidate it. Then, if when you test, the test is negative, you've actually created some support for your hypothesis. (negative and positive being interchangeable here, i.e. if you were to test for an absence of wheat residue, then the presence of wheat residue would be negative result). The you've got to be thinking about what your controls will be. A lot of comparable Wiltshire chalkland will have been used for wheat production at some point. Even currently wild looking bits such as Fyfield Down were once farmlands.
I'll wish you the best of luck though Clyde, partly 'cos I think you're gonna need it, and partly 'cos I'd love to see such a truly unlikely and highly peculiar construction be shown to have actually existed. It would almost qualify as Forteana. Also 'cos you've obviously put a lot of thought, effort and imagination into it. If it turns out you decide it is all a bit far-fetched, then I hope you find/think of something else to ponder :)
