OLDING AND FAULTING IN THE EARTH ?S CRUST 4.2 Fold mountains in Ireland Before folding
The Munster ridge and valley province
Between 350 and 400 million years ago Ireland lay closer to the equator and experienced a dry desert climate. Huge amounts of sand were deposited in the south and south- west of Ireland. Today this is known as Old Red Sandstone. Later, a muddy sea covered the area and limestone was laid down.
About 300 million years ago the rocks of Ireland were squeezed by earth movements, creating fold mountains. These foldings are known as Armorican folds. Similar fold mountains occur in southern England and Brittany in France.
These fold mountains stretch from Waterford to Kerry. The east-west trending anticlines, or ridges, are responsible for mountains such as the Comeraghs, Silvermines and Galtee Mountains. These ridges are made of resistant sandstone rock. During folding,
rocks in the
anticlines were stretched and cracks formed, weakening the limestone. Over time, weathering and erosion removed the limestone from the anticlines exposing the sandstone beneath.
Today the fold synclines are still covered with this limestone and form broad valleys. The Golden Vale and the Blackwater Valley are examples.
Areas of few folds
Limeston Compressio Compressio
Sandstone During folding 300 million years ago More
weathering of
limestone
Folding causes splits in anticlines allowing water into rock
Today, after weathering and erosion Sandstone
Limestone covered valleys
Anticline Syncline
Fig. 6 Exam diagram: The formation of the Munster ridge and valley province.
Direction of plate movement
Pressure
gradually decreases
Areas of intense folding and mountain
Direction of Fig. 7 Location map of Munster ridge and valley province 57