Bucks Earth Heritage Group

Lambeth Group

Tertiary deposits are only found to any large extent in South Bucks. Loose blocks of hard sandstone locally known as ''Sarsen stones'', Denner Stone or Puddingstones can be found in small clusters throughout the Chilterns. They represent an ancient river deposit, which was lain down during the early Tertiary (58-55 million years ago) in a semi-arid warm climate. The rocks are referred to as Silcretes, as they have a silica (quartz) cement and are very hard. They can range from coarse sandstone to conglomerates containing rounded black /red coated flint pebbles. At Bradenham village, large blocks occur and it has been estimated that the formation was between 2 to 6m in thickness. The blocks may once have formed a continuous bed across the district but because of the subsequent erosion and the freeze thaw activities of the ice ages, the beds have been eroded and sludged their way down slope by a process called solifluction. It is possible that they could be found in situ however no definitive locations have been identified.

Puddingstone bolder on display at the roundabout in Princes Risborough below

Bradenham sarsens in the field where they have lain since the end of the Ice Age. This local form is known as the Bradenham Puddingstone.

The stone has also been used by locals for some time (see the block used in the church of St Botolphes in the village). The colourful flint pebbles of this stone are very clear here.

The church tower and its buttress at Bradenham are made of local stone: flint, sandy sarsen (Denner Hill type), local Bucks Portland Limestone, with buttress corner repairs of Portland limestone from Dorset (probably Victorian)