Clarehill ASSI

Clarehill is a special place because of its earth science interest.  The area provides access to a sequence of limestones exposed in the disused quarry.

Clarehill provides exposure of a series of named units (referred to by geologists as Members) of rock within the Cretaceous chalk known as the Ulster White Limestone. These rocks formed in warm water conditions and are made up of the skeletal remains of microscopic organisms which lived in the sea at that time.

Clarehill exposes all Members of the Ulster White Limestone from the Garron Chalk Member (the oldest rocks at this site) to the Tanderagee Chalk Member so includes (from bottom to top) the Garron, Portrush, Ballymagarry and Tanderagee units. However, the lower 8 Members of the Ulster Limestone, known from elsewhere, are not present here. This indicates that the area formed high ground, was unlikely to be a depositional site and hence does not contain rocks from the earliest Ulster White Limestone period. It was only later that chalk was deposited here and even then the chalk units are relatively thin when compared with elsewhere in Northern Ireland.

The Ballymagarry Chalk Member is of particular importance here. Some 13 metres thick it is characterised by a large increase in the amount of flint present in the chalk. These often take the form of numerous large barrel shaped flints known as paramoudras.

The term paramoudra was first introduced into geology from this district in the early 19^th century by the eminent geologist William Buckland. Its origins are not clear but may be derived from an Irish word, probably padhramoudras ‘ugly Paddies’ or peura muireach ‘sea pears’. The formation of paramoudras was originally thought to be associated sponges (with the sponge acting as a nucleus for these unusually shaped flints) but they are now regarded to be of inorganic origin

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