"Dalradian" is the name given to a series of metamorphic rocks in both Scotland and Ireland. One unit, known as the "Boulder Bed," is thought to be of glacial origin and generally is correlated with the bodies of similar origin in the Eocambrian of Scandinavia; sedimentation may have continued into Cambrian time. Evidence from Ireland suggests that the Dalradian was metamorphosed prior to the deposition of the Arenig.

It is possible to correlate the Dalradian successions with those in Scotland. In Donegal, north of the Main Donegal Granite, the Creeslough Succession corresponds to the Ballachulish Succession of Scotland; south of the granite, the Kilmacrenan Succession corresponds to the Islay Succession and contains the Boulder Bed at its base. The Creeslough Succession is folded into a recumbent syncline overturned to the northwest, and the Kilmacrenan Succession is folded into a recumbent syncline overturned to the southeast. These large folds are of F₂-F₃ generation; no large-scale F₁ folds have been found, and post-F₃ phases are represented in general by a series of small angular folds. The rocks of these successions are a mixed sequence of quartzite grit, limestone, and pelite; metamorphosed dolerite is common throughout. Southeast of the Leannan fault, which is a possible continuation of the Great Glen fault of Scotland, is a succession that contains the Boulder Bed but otherwise is quite different from the Kilmacrenan Succession. It is reasonable to correlate the two in general terms and to suggest that they are younger than the Creeslough Succession.

The grade of metamorphism is generally low, but increases on the southeast side of the Leannan fault and around the granites.

Two Dalradian outcrops are present in Northern Ireland. One is a natural continuation of outcrops in Donegal and forms the Sperrin Mountains; poor exposure makes correlation difficult, but these rocks seem to belong to the Kilmacrenan Succession. The other group, in County Antrim, can be correlated readily with the Kilmacrenan and Islay Succession.