Like most people I suspect, I know very little of Marden Henge other than it is/was larger than Avebury and also had a setting of circular stones now disappeared. It will be interesting to see if it predates Avebury and if it did what would be the odds of Marden's stones ending up at Avebury? That would set the cat amongst the pigeons wouldn't it! Just a thought but an interesting one nevertheless!