It is a region of quiescence or of faulting, but not of folding.
The ranges are primarily the result of faulting and uplifting of large blocks of the earths crust.
Faulting, however, is by no means absent, and some of the faults are of considerable magnitude.
The effect of such folds is often exaggerated by thrusts, and faulting of this sort is prominent in the southern section, where the existence of over-thrusts measured by several miles has been established.
Faulting, probably in Pliocene times, lowered the basaltic plateaus to form the basin of Lough Neagh, leaving the eastern scarp at heights ranging up to 1800 ft.