Faulting is a term used in geology to describe how earth movements may produce a displacement or fracturing of part of the earth’s surface. As a result, unlike rocks may end up beside each other.
Faults can be both minor and major in scale. In Ireland, two of the great fault lines are those of the Highland Boundary Fault and the Southern Uplands Fault. These lines can be traced from Scotland (where the names originated) through Ireland, and on the other side of the Atlantic, through Newfoundland. They appear to represent the boundaries between major sections of the geological basement called 'terranes'.
A map has been constructed to show the 'terranes of Ireland', meaning the fundamental pieces of crust that would be exposed if the rocks formed over the last 400 million years were stripped off.