Robert Wood Williamson was the owner of Fletcher Moss Gardens and the associated house, The Croft, where he designed the rockery.
There is also mention of Williamson in 'Country Life' http://www.countrylife.co.uk/culture/article/66677/Garden_Magic.html. as he lived in a Lutyens house, Copse House at Brook, near Godalming, Surrey, with a garden designed by Gertrude Jekyll in 1912-13.