Brecon Beacons National Park

Within Fforest Fawr Geopark you'll find all sorts of different rock types.  There are sandstones and mudstones, there are siltstones and limestones, there are gritstones and coals.  All of our rocks are sedimentary rocks, that's to say they were laid down grain by grain as sediment either by water - in rivers or the sea - or by wind.

Mudstones and sandstones

The northern part of the Geopark is underlain by rocks of  Ordovician and Silurian age which consist largely of mudstones, sandstones and siltstones.

The Old Red Sandstone

The spectacular mountains of Fforest Fawr, the Black Mountain and the Brecon Beacons are formed by a thick pile of sandstones and mudstones which geologists refer to collectively as the Old Red Sandstone.   Look closely at these rocks and you can see the individual grains of sand.  The colours come from different minerals in the rock - the redness comes from the high amount of iron oxides within these desert sandstones.

Carboniferous Limestone

Along the southern flanks of the mountains are tracts of interesting country where the rock beneath your feet is limestone.  Formed in shallow sea when Britain lay on the equator, it consists largely of the countless skeletons of plants and animals.  Most are too small to see with the naked eye although larger fossils are to be found in some locations.

Millstone Grit

The Millstone Grit gives rise to equally interesting countryside, often rough and rocky.  These are coarse-grained sandstones whose source lay far to the north.

Coal Measures

The Coal Measures consist of mudstones with the occasional band of harder sandstone.  Some of these give rise to spectacular waterfalls in the south of the Geopark.