Ancient Oceans and Mighty Mountains

The oldest widespread rocks of Northern Ireland form the uplands of the Sperrins and north-east Antrim. These hills are the remains of an ancient mountain chain, once larger and higher than the Himalayas are today. Formed from sediments laid down in basins on the American side of a long disappeared ocean known as the Iapetus, they show that not only did part of Ireland once form part of that continent, but also that tremendous collisions have occurred, producing mountains out of materials formed on ocean floors.

Other sediments which accumulated on this ancient ocean floor have been preserved as the extensive series of ordovician, silurian, sandstone and shale, forming the lowlands of Down and Armagh. Once again, evidence contained in these rocks shows that they actually represent sections of the seabed which originated from the American side of this lost ocean. During a second phase of mountain building, granitic rocks were emplaced below the earths surface. Erosion has exposed these, and can be seen today as the uplands which include Slieve Croob. Slieve Gallion mainly dates from this period.