Stratigraphic column

Geological time is divided into a sequence of Periods.

Key Periods in Irish geological history

(Click scenes for detail).

Palaeogeographic maps

Maps of the Earth as it was millions of years ago (click maps for detail).

Quaternary. In the last two million years during the Ice Age the climate has been either very cold with ice sheets and glaciers, or warmer when Mammoth, Giant Irish Deer and Brown Bears roamed the countryside. The last ice melted 10,000 yearsago and man arrived in Ireland 5,500 years ago.

Tertiary. Deposition of clay occured around Lough Neagh. Climate warmer than today. Volcanic activity in north-east Ireland produces lava that forms the Antrim Plateau and cools to form the Giant's Causeway.

Cretaceous. Dinosaurs become extinct at the end of the Cretaceous when a large meteorite hits the Earth. Chalk, a pure white limestone was deposited in warm seas. It is now preserved in north-east Ireland and with a small patch in Kerry. There may have been dinosaurs in Ireland at this time, but we have little evidence of this as much of the Cretaceous rocks have since been eroded away.

Jurassic. Ireland was covered by shallow seas in which the marine reptiles ichthyosaurs and plesiosaurs lived, together with bony fishes and ammonites. Muds and sandstones were deposited. Today some Jurassic rocks can be seen along the Antrim coast; elsewhere they have been eroded away.

Triassic. Ireland was a hot, desert-like continent in which sandstones (New Red Sandstone) was deposited. Salt deposits formed in shallow salty lakes. Today Triassic rocks occur near Kingscourt in Co. Cavan where the salt mineral gypsum is quarried for plasterboard and cement.

Permian. During the Permian the seas retreated and Ireland was land. Most Permian rocks are now eroded away. When Africa
collided with Europe the crust was crumpled, and valleys formed in Kerry, Cork, and Waterford, running from east to west.

Carboniferous. In the Upper Carboniferous the sea was replaced by swamps containing forests of tree-ferns and cycads where amphibians and insects lived. These plants eventually formed the coal once mined at Arigna, Co. Leitrim, Castlecomer, Co. Kilkenny, and Kanturk, Co. Cork. At the beginning of the Lower Carboniferous a tropical sea slowly moved northwards and covered the land. Reefs and limestone formed in this sea,
and many animals were preserved as fossils. Limestone now covers over 50% of Ireland.

Devonian. Ireland was part of a large dry desert continent. Large rivers flowed through it from north to south and drained into a shallow sea in the south of Ireland. Sand and coarse pebbly sediments formed the Old Red Sandstone, best seen in Counties Cork and Kerry. Fish dominated the oceans. Some mountain-building activity produced folds and faults.

Silurian. Volcanic islands erupted lavas and volcanic ash near Dingle, Co. Kerry. Shallow seas contained corals, brachiopods, and trilobites, and plants grew on dry land for the first time. The Leinster granite was injected into the crust.

Ordovician. Slowly the Iapetus Ocean closed as the contents moved closer together. Small volcanic islands appeared in Counties Mayo, Longford, Down, Waterford and Dublin and lavas and volcanic ash were dumped into the shallower sea, together with mud and sand from the land. Some limestone formed in this sea which can now be found in Mayo, Wexford and

Cambrian. Two large continents were separated by an ocean called Iapetus and what is now Ireland was under this closing sea. Fine-grained sediments were deposited and can now be found at Bray Head and Howth as sandstones and slates. Some of these rocks include trace fossils (burrows and trails) and include Oldhamia which help date the rocks

Precambrian. This was a long time period when much of the Earth's surface was unstable. Rocks such as limestone and sandstone were deposited and later these were altered by metamorphism to marble, quartzite and schist. Various igneous rocks were intruded. The oldest rocks in Ireland are 1,700 million years old and are found on Inishtrahull Island, Co. Donegal.








2009. Site designed by Adam Stuart Smith and Patrick Wyse Jackson.