Scheduled Monuments in Pembrokeshire Scheduled Monuments in Pembrokeshire Pembrokeshire is the fifth-largest county in Wales, but has more Ancient Monuments (526) than any except Powys. This gives it an extremely high density of monuments, with 33.4 per 100km2. (Only the tiny County Boroughs of Newport and Merthyr Tydfil have a higher density). With three-quarters of its boundary being coastline, Pembrokeshire occupies the western end of the West Wales peninsular, terminating with the tiny cathedral city of St David's. It was a historic county in its own right but between 1975 and 1996 it joined Carmarthen and Ceredigion in the much larger county of Dyfed.
Pembrokeshire to its proximity to the relatively warm Atlantic Ocean. Inland, average temperatures tend to fall 0.5 °C for each 100 metres increase in height. The air pollution rating of Pembrokeshire is "Good", the lowest rating. The rocks in the county were formed between 600 and 290 million years ago. More recent rock formations were eroded when sea levels rose 80 million years ago, at the end of the Cretaceous Period. Around 60 million years ago, the Pembrokeshire landmass emerged through a combination of uplift and falling sea levels; the youngest rocks, from the Carboniferous Period, contain the Pembrokeshire Coalfield. The