Exploring West Sussex geology
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The Lower Greensand Group

The Hythe Formation is well exposed in the quarry at Little Bognor. The rock is made up of soft and hard sandstones with layers of chert, a hard grey stone made of silica. Fossils are rare and difficult to find but represent a true marine environment. Bivalve and brachiopod shells, sea urchins (echinoids) and ammonites have been found.

The Sandgate Formation is poorly exposed in the sides of sunken lanes. It is a complex deposit made up of beds of soft sandstone (such as the Pulborough Sandrock) and clay (Marehill Clay). The Sandgate Formation is rarely fossilferous. It was formerly dug near Marehill for use as moulding sand in iron casting. The old mines are now a Sussex Wildlife Trust site for bats and can only be visited under supervision at certain times of the year (please contact me). The site is not open for public access.

The Folkestone Formation is worked extensively for building sand. Many old pits can still be discovered although exposures of these soft sands rapidly deteriorate when left to weather. Clean surfaces often show cross- or current-bedding, effectively sections through huge sand waves formed on the sea floor. Fossils are rare due to the active conditions in which the sands were deposited.


The green of greensand is caused by grains of the mineral known as glauconite. It is an iron potassium silicate with the chemical formula (K,Na,Ca)1.2-2.0(Fe3+,Al,Fe2+,Mg)4(Si7-7.6Al1-0.4O20)(OH)4·7 nH2O. Glauconite forms in the surface layers of marine sediment on the sea floor within 10,000 to 100,000 years of deposition. In West Sussex, it is not always present in enough quantity to colour the sand a true green, but is commonly known elsewhere.