Wealden Sandstones and Clays – Lower Cretaceous (lead authors JT &WGT)
The Wealden Group is a multi-coloured sequence of sands, silts and clays deposited in lakes, rivers and deltas 146-125 million years ago, overlying the Purbeck Group.
These strata outcrop in the area between Swanage (thickest) and Durdle Door, bounded to the north by the Chalk ridge and to the south by the Purbeck hills. They are best exposed at Swanage, Worbarrow Bay and Lulworth Cove.
There are also occasional concretions within the clays, of similar colour, but smoother in texture. Both these rock types have been used in field walls and the foundations of cottages in the vale. Near Swanage, Wealden clay is used for brickmaking.
Some coarse pebbly ”gritty” sandstones form ridges in the vale, such as Windmill Knap (near Swanage) and Corfe Common where the “Coarse Quartz Grit” was once quarried. This is a hard ferruginous sandstone, of a purple to blood-red colour, containing minerals derived from erosion of the Dartmoor granite. (see image below)
Text JT & GT Mar 2017