And a chamber may have collapsed and its contents deposited elsewhere. Or a chamber may have collapsed, stayed in place and been filled with material from above. We'll never know until more sophisticated tomographical/volumetric techniques are available. Then what? If what looks like a chamber is discovered then an excavation is on the cards meaning further tunnelling, and as much as I hate that idea the possibility of advancing our understanding of Silbury and the possibility of learning more about the people who built it won't/can't be ignored.

M'be the last word on that should go to A C Smith himself, "I would bespeak the respect of all Wiltshiremen for Silbury, which deserves our reverence from its antiquity, our admiration from its size, and our awe from the mystery which envelopes it."