Geology of the North - Co. Antrim & Co. Down
Unlocking the rocky secrets of County Antrim and County Down - a tale of tropical seas, deserts, volcanoes and dinosaurs …
You don't have to travel
far in Northern Ireland to see a wide range of breath-taking scenery - from
the Giant's Causeway to the Mourne Mountains. Northern Ireland's landscape is
controlled by its underlying rocks, formed over hundreds of millions of years
as the country slowly drifted northwards across the face of the Earth.
The rocks of Co.Antrim and Co.Down are very different. Co.Antrim is dominated
by black volcanic basalts and white chalk, whereas Co.Down consists mostly of
red sandstones, black mudstones, slates and schists. We can use these rocks
to work out the environment in which they originally formed, and to develop
an understanding of how these counties, and Northern Ireland as a whole, formed
over time.
County Down
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The oldest rocks in Co.Down are 417-495 million years old and consist of mudstones and volcanic rocks. At that time Co.Down lay beneath a deep ocean, on the edge of an ancient continent made up of Scotland, north America and the north of Ireland. A huge ocean separated this continent from the rest of Ireland, England, Wales and Europe. Over millions of years, this ocean closed and the two ancient continents collided, baking the rocks to form slates and schists (e.g. at Bangor).
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A long time-gap separates these ancient rocks from the next series, which formed about 280 million years ago, when Northern Ireland lay at about the same latitude as today's Sahara Desert. Examples of red sandstones and mudstones from this time occur in the Lagan Valley and around Dundonald and Comber.
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| Finally, about 63 million years ago, the Mournes and Slieve Gullion formed at a time when Northern Ireland was covered by active volcanoes. These mountains are the remnants of major volcanic centres which erupted when the land rifted apart during the opening up of the north Atlantic Ocean. | |
County Antrim
The oldest rocks in County
Antrim are 700-550 million years old and are found around Ballycastle and Cushendun.
These rocks have been baked and squeezed to form metamorphic schists and gneisses.
A long time-gap occurs between such ancient rocks and the next series found
at Cushendall and Cushendun. These rocks (red sandstones and mudstones) are
about 380 million years old and formed in an ancient desert, when Northern Ireland
lay much further south than at present. In the same area we also find coal (which
was mined until 1967). The coal formed in subtropical swamps (similar to the
mangrove swamps of the Florida Everglades) about 340 million years ago.
Over time, Northern Ireland slowly drifted northwards and by about 200 million
years ago, when dinosaurs ruled the Earth, Co.Antrim and Co.Down lay submerged
beneath a warm, shallow, subtropical sea (similar to the Bahamas). These conditions
allowed fine mudstones and limestones to form, examples of which can be seen
at Portrush (where they contain many fossil ammonites).
By approximately 120 million years later, a deeper sea covered the area and
thick, white chalk (made up of billions of microfossils, too small to see with
the naked eye) was deposited.
Finally, about 63 million years ago, Co.Antrim became a very violent, volcanically
active area (similar to Iceland today). Flows of hot basaltic lava were periodically
erupted across the land as the Atlantic Ocean rifted open. This vast amount
of volcanic activity not only produced the Antrim flood basalts, but also released
huge amounts of noxious gases into the atmosphere. Similar volcanic activity
occurred all over the Earth, and it is thought that the extinction of the dinosaurs
at this time probably resulted from a combination of volcanic ash and gases
blocking out the sun and a catastrophic collision of the Earth with a gigantic
meteorite.
