Oh, and I see that one of our authors - Jim Leary - discovered a "sunken floor" in the foundations of the Marden Henge (of which only the bottom 15 cm remain), purpose unknown. Hmmm: was it the equivalent of a mortuary slab?
Finally: for a scientific hypothesis or theory to have value, it must have predictive utility. OK. I predict that the darker soil seams in that hill will be enriched in the chemical elements that are in human tissue. The soluble ones will probably have leached out, but given the alkaline conditions that pertain in chalk, I suspect there may be elevated levels of iron, deposited or precipitated as iron (III) oxide or hydroxides. Note the earlier comment/link re the 'iron pan' formation, which may simply be a consequence of local geology, or there again, maybe not.
It is also possible that there is still "fossil" carbon in the dark-coloured soil if the equivalent of plant humus. Radiocarbon-dating, matched against appropriate controls from non-dark clay and other debris could point to an exceptional contribution from a Neolithic carbon-rich source.
Could it be that ritualistic evisceration("cleansing") of the recently deceased was a de rigeur convention ("fashion statement") for a brief period (a century or thereabouts) in progressive Neolithic society? Or there again, a monument that contained the hearts of the deceased (and much else besides) may in time have come to be seen (from afar)as a powerful symbol of the continuity of life and society. Maybe the heart and soul were perceived as one for that brief period of history.
My theory for Silbury Hill: it served as a communal organ reliquary, or, more picturesquely, as a visceral Valhalla.
Colin Berry, aka sciencebod May 17, 2012