The Usk Inlier is a domed outcrop of rock strata of

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

age in

Monmouthshire Monmouthshire ( cy, Sir Fynwy) is a county in the south-east of Wales. The name derives from the historic county of the same name; the modern county covers the eastern three-fifths of the historic county. The largest town is Abergavenny, with ...

in south-eastern

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. It is located in the countryside between the towns of

Caerleon Caerleon (; cy, Caerllion) is a town and community in Newport, Wales. Situated on the River Usk, it lies northeast of Newport city centre, and southeast of Cwmbran. Caerleon is of archaeological importance, being the site of a notable Roman ...

and

Pontypool Pontypool ( cy, Pont-y-pŵl ) is a town and the administrative centre of the county borough of Torfaen, within the historic boundaries of Monmouthshire in South Wales. It has a population of 28,970. Location It is situated on the Afon Lwyd ri ...

and the village of Raglan. The longer axis of the dome or ' pericline', often referred to as the Usk Anticline, is aligned north–south. The

inlier An inlier is an area of older rock (geology), rocks surrounded by younger rocks. Inliers are typically formed by the erosion of overlying younger rocks to reveal a limited outcrop, exposure of the older underlying rocks. Fault (geology), Faulting o ...

is largely surrounded by a sequence of

Old Red Sandstone The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also exte ...

rocks of

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

age, though both these and the Silurian rocks are largely obscured by superficial deposits.British Geological Survey 1:50,000 scale geological map sheets 232, 233, 249 & 250 (England & Wales series)

References

Anticlines Landforms of Monmouthshire Geology of Wales Rock formations of Wales {{Wales-geo-stub