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
Waterford.
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.
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