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The White Rocks

The "White Rocks" is the name given to cliffs to the east of Portrush in County Antrim, Northern Ireland. These cliffs are made of chalk, or Ulster White Limestone as these deposits are termed by geologists. Chalk is a pure form of limestone and, in the case of the White Rocks, is Cretaceous in age, laid down on beds of Hibernian Greensand between 142 and 65 million years old. When the chalk was laid down, this part of the globe was a warm shallow sea. In this sea thrived tiny single celled organisms called coccoliths, the skeletons of which built up on the sea floor. Chalk CliffOver time this accumulation was compressed to form the chalk we can see today. Courses of flint can be seen running through the chalk, as the photograph illustrates. However, unlike the chalk laid down in similar conditions in South England, this chalk is very hard.

The Cretaceous chalk can be seen in many parts of North East Ireland, but its traces have been eroded elsewhere. The reason it has survived in County Antrim is because of the cap of basalt, which was produced by eruptions from fissures in the earth's crust. These had been created as the Atlantic Ocean opened between North America and Europe from about 65 million years ago. The chalk now is visible below the basalt at the White Rocks, on the Cave Hill in Belfast, around the County Antrim Coast Road and at Limavady, County Derry.

About 120 metres of chalk can be found in the north coast of County Antrim today although not all in one place — where local erosion or a lack of deposition ocurred, some levels within the chalk will be absent. The thickness beneath the basalt 'cap' is not known although the Aughrimderg Borehole gave a result of 150 metres. However this may be a result of faulting, which might have repeated some of the rock sequences.

The chalk rocks are rich in fossils. Some of the flints are preserved and perfectly formed echinoids. There are also belemnites of various kinds. These cigar-shaped fossils are the remains of the internal skeletons of octopus-like creatures, the soft parts of which have not been preserved.

Close-up of flint in chalk

The outcrops of chalk in County Antrim have been of economic value for a considerable time. Early people used the flint to make weapons and other tools. Many sites with worked flints have been excavated, especially around the coast of County Antrim. There have been a number of excavations in Larne and in the Glens of Antrim where the raised beach appeared to have been the site of early 'industrial' working of flint implements. Perhaps it was the flint that first attracted Mesolithic people to Ireland some 8000 years ago - their first known habitation was in Mountsandal close to Coleraine and not far from the flint from which they made their tools.

In the last century the chalk was burned in kilns to produce quicklime for spreading on fields. This reduced the acidity of the soil and did much to improve the productivity of agriculture. The remains of these kilns are still dotted about, close to chalk outcrops. The chalk is still being used productively. A quarrying operation in Glenarm, in the Glens of Antrim, produces chalk which is used for a wide range of industrial purposes - including acting as a constituent in toothpaste and in the white lines painted on roads all over Europe.