Antrim's coast provides the most varied of geological panoramas in Ireland. There are white Chalk cliffs near Portrush where the sea has carved from them the Wishing Arch. Basalt lavas cover most of the plateau inland and appear coastally with their exquisite honeycomb jointing, which has made the Giant's Causeway scenically famous. Beneath these formations is the soft, grey Lias Clay which, turgid with ground water, has heaved and flowed in a variety of spectacular landslides from Larne northwards, capsizing great blocks of the massive rocks above.
The county's north-eastern corner is different once again. There the flat Carboniferous formations are warm yellow sandstones, interbedded with black seams of coal high up on the nearer slopes, where adits (or shafts) have been driven horizontally into the cliffs to work them. This view looks north-eastwards from near Ballycastle across to Fair Head, where a thick sheet, or sill, of the dark basaltic magma injected itself along the Carboniferous strata. Its vertical joints now outline the cliff faces and a great scree of fallen-away dolerite boulders slopes down from the foot of it.
The high ground above is flat moorland with a crannog-studded lake or two. Desolate now, it nonetheless supported flourishing agricultural communities in Neolithic and later times, their farming and settlement patterns abundantly preserved under the peat. The cliff coast is the haunt of sea birds and, in particular, raptors, for there the golden eagle has nested in recent years and buzzards are regularly to be seen.
Glossary of terms
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Basalt A dark, fine-grained lava formed by the solidification of molten igneous magma.
Bedding Refers to the layers often present in sedimentary rocks (also known as Stratification). A bedding plane is the surface separating one layer from another.
Carboniferous Geological period which began approximately 345 million years ago and lasted for about 65 million years.
Dolerite A medium-grained igneous rock similar to basalt.
Lias Clay Geological formation beginning around 195 million years ago and lasting 15 million years.
Magma Molten rock material which forms igneous rocks on cooling.
Sedimentary Rock Formed by accumulation of detritus transported by water, wind or ice or by precipitation from solution (e.g. limestones).
Stratification - see Bedding.
from the Appletree Press title The Irish Landscape by James C. Brindley