(4540 – 542 million years ago)
No rocks of this age are known to be exposed at the surface within Fforest Fawr Geopark though they will certainly exist at great depth.
The nearest exposures of rocks of this age are to be found in Pembrokeshire to the west, at Stanner Rocks (702 million years old) near the English border to the northeast at Kington and in the area of the Malvern Hills in England to the east. Wales’ oldest rocks – all Precambrian and up to 800 million years old – are found on Anglesey and celebrated as part of GeoMon -Anglesey’s Geopark.
What’s in a name?
The term ‘Precambrian’ was originally used to refer to any rocks older than the Cambrian Period. Unlike the Cambrian, Silurian etc it is not a ‘period’ nor is it strictly an ‘era’ in the formal geological sense. The Precambrian accounts for 90% of the age of the Earth and is nowadays subdivided into many ‘eons’.