Exploring West Sussex geology
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The Selborne Group

The Gault Formation is a fossiliferous grey clay, which is only exposed where it has been dug for brick-making. Former clay pits are mostly overgrown, backfilled or flooded. The only exposure (illustrated) is on private land associated with Pitsham brickworks near Midhurst. Access is not permitted and fossils are very rare. The former clay pit at Small Dole (a landfill site for many years) produced abundant fossils, including ammonites, belemnites and many other marine fossils.

The Upper Greensand is exposed in sunken lanes and river cliffs to the north of the South Downs. It is a grey, lime-rich, fine-grained silty sandstone with few fossils (mostly bivalve sea shells). This exposure in the river cliff near Amberley Castle is one place where the Upper Greensand can be inspected that isn’t at a roadside.

Upper Greensand is best seen in the many churches along the outcrop of the rock. It often weathers with a brown surface over the grey stone beneath. This church at Elsted has both grey and brown-weathering Upper Greensand. The village of South Harting is predominantly built of this stone.

Malmstone or clunch

The Upper Greensand of West Sussex is correctly given a traditional common name of malmstone, malm meaning ‘chalky rock’. It is also incorrectly called clunch in the description of building stone. Clunch is strictly a type of chalk, the name having been applied to the lower beds of the Chalk in East Anglia and Cambridgeshire. It has also been used to describe a chalk from near Lewes.

 

Clunch (geologically) is not Upper Greensand and use of the word in West Sussex is not appropriate. Malmstone is a perfectly acceptable name!