250 Million Years Ago
The Last 300 Million Years – After the Carboniferous
Cracks in the bedrock were formed and were “plugged” by limited intrusions of magma in our geopark area, as seen by the dolerite sill on top of the Partry mountains at Droimchogaidh. This rifting activity that separated Ireland from Greenland and North America is also now thought to be responsible for the formation of the mountains that we see today in the west of Ireland. A section of Carboniferous sandstone that predates the Carboniferous limestone of Ireland is found on top of the Maumtrasna plateau, which sits 400m above the sea level. The same sandstoneis also found at a depth of 300m below the surface around Clonbur. This indicates that the rocks west of Lough Mask and Lough Corrib were uplifted by about 700m. This would have occurred when the early spread of oceanic crust pushed the two landmasses apart, which would have locally pinned blocks of bedrock against one another in a limited space and pushed them upwards.