Great Plat under construction with the morte slate retaining walls on the south (Pergola) and east (East Rill) sides now almost complete, 1904. Photo by Ivo Richard Vesey (1881-1958), 5th Viscount de Vesci.

The silvery-grey morte slate used throughout the Formal Garden by Edwin Lutyens was quarried on site, mainly in the two combes (valleys) to the north of the House, but the Hestercombe quarries were also the source of a rarer, and more decorative, stone. Pink diorite was used to reface the west front of Hestercombe House on at least one occasion in the 1720s when John Bampfylde (1691-1750) commissioned a classical ordering of sash windows, diorite surrounds, and neatly coursed diorite with the aim of creating a fashionable Palladian facade.