Unconformably overlying the rocks of the Pebidian, the following sequence has been established (youngest/uppermost at top): These strata are well-displayed in the coastal cliffs at St Justinian's and between Porthllisky and Newgale though exposures inland are less frequent.
An outcrop including the Portfield, Haverford Mudstone and Gasworks Sandstone formations extends east-west beneath Haverfordwest and out to Narberth.
The Skomer Volcanic Group comprises a succession of extrusive igneous rock dating from the Aeronian stage of the Llandovery.
To the south they form a band of higher ground from Rat Island at the mouth of Milford Haven waterway, east-southeast via Hundleton to Old Castle Head near Manorbier.
Lying stratigraphically above the Pridolian age strata are those units of the Old Red Sandstone laid down during the Devonian period (419-359 Ma).
A major calcrete exposed in the cliffs at the southern tip of the island is named the Chapel Point Limestone Member.
The Carboniferous system (equating to 359-299 Ma) is represented by four broadly parallel outcrops of the Carboniferous Limestone in the south and southeast of the county, between the more northerly two of which are outcrops of the Marros Group strata and the lower and middle Coal Measures, extending west to the shores of St Brides Bay.
The most extensive outcrop of the limestone is in the southernmost part of the county where it forms almost continuous coastal cliffs between Stackpole Quay and the south end of Frainslake Sands.
These strata extend in a band of country from Ragwen Point west-northwest via Marros Mountain (the locality of Marros, after which the sequence is named, is just in Carmarthenshire to the east of the national park) to Picton Park on the Eastern Cleddau and then west and northwest to reach St Brides Bay at Haroldston West.
A further band extends from the northern edge of Tenby towards Redberth and via a narrowing outcrop to Llangwm on the western side of the Daugleddau.
It is possible that the entire area lay beneath sea level during Cretaceous times but any evidence of chalk strata from that period has since disappeared.
[5] The geology of Ramsey Island is complex and comprises a mix of late Cambrian and Ordovician igneous and sedimentary rocks which have traditionally been assigned different names from their mainland counterparts.
In the south are the Ritec and Benton faults which, along with various fold axes affecting the late Palaeozoic succession, have an east-west to ESE-WSW alignment.
A major system of glacial meltwater channels extends around the coastal zone between the Teifi estuary and Fishguard, north of the Preseli Hills.
Solva Group sandstones were quarried in the C12th at Caer Bwdy for decorative work in nearby St Davids Cathedral.
Though marketed as 'granite', it was an intrusion of dolerite of Ordovician age which was also formerly worked at Jerusalem Quarry, Porthgain and the legacy of that extraction and of the locally sourced slate and their export from the harbour prior to 1931 is now a visitor attraction.
The Pembrokeshire Coast National Park was designated in 1952 principally on account of its spectacular coastal scenery which reflects the diverse geology from which it has evolved.
Coasteering is a sport which has grown popular around the coast of the National Park in recent years which makes use of the abundant coastal cliffs.