>One more thing - they made a big thing about it being a massive, impressive, white, chalky henge - how long would it have remained white before grenery started to grow on it? I'm thinking of chalk cuttings for roads, etc - they seem to grow back quite quickly...<

Yeah, this was discussed in relation to Silbury and Avebury. Seem to remember it was a really short period - something like ten years or so?