The Farewell Rock is the name given to a series of sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

s which lie at the boundary of the Coal Measures

Coal Measures

The Coal Measures is a lithostratigraphical term for the coal-bearing part of the Upper Carboniferous System. It represents the remains of fluvio-deltaic sediment, and consists mainly of clastic rocks interstratified with the beds of coal...

 with the underlying Marros Group

Marros Group

The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous period in South Wales. These rocks were formerly known as the Millstone Grit Series but are now distinguished from the similar but geographically separate rock sequences of the Pennines and...

 in South Wales

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

. Once thought to be a single sandstone, it is now accepted that the same name has been applied to several different sandstones of similar age across the South Wales Coalfield

South Wales Coalfield

The South Wales Coalfield is a large region of south Wales that is rich with coal deposits, especially the South Wales Valleys.-The coalfield area:...

. The sandstone unit known as the Farewell Rock in the Pembrokeshire Coalfield

Pembrokeshire Coalfield

The Pembrokeshire Coalfield in West Wales is one of the smallest British coalfields. The main coalfield extends from Saundersfoot on Carmarthen Bay westwards to Broad Haven on St Brides Bay...

 is continuous with the Cumbriense Quartzite of the main South Wales Coalfield. These are assigned to the uppermost part of the Marros Group (the former Millstone Grit Series

Millstone Grit

Millstone Grit is the name given to any of a number of coarse-grained sandstones of Carboniferous age which occur in the Northern England. The name derives from its use in earlier times as a source of millstones for use principally in watermills...

) which is of Namurian

Namurian

The Namurian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 326 and 313 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Namurian is named for the Belgian city and province of Namur where strata of this age...

 age. In the South Wales Coalfield, the name is given to a thicker, overlying (and hence younger) sandstone unit which, though formerly assigned to the Millstone Grit Series, is now assigned to the Lower Coal Measures which are of Westphalian

Westphalian (stage)

The Westphalian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 313 and 304 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Westphalian is named for the region of Westphalia in western Germany where strata...

 age.

The name is said to have been coined by ironstone

Ironstone

Ironstone is a sedimentary rock, either deposited directly as a ferruginous sediment or created by chemical repacement, that contains a substantial proportion of an iron compound from which iron either can be or once was smelted commercially. This term is customarily restricted to hard coarsely...

 miners who once worked the siderite

Siderite

Siderite is a mineral composed of iron carbonate FeCO3. It takes its name from the Greek word σίδηρος sideros, “iron”. It is a valuable iron mineral, since it is 48% iron and contains no sulfur or phosphorus...

 deposits which stratigraphically

Stratigraphy

Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....

 overlie this rock unit. Digging beyond ie deeper than this bed would yield no further iron ore and so, on reaching it, they could bid a 'farewell' to further riches. The name was subsequently adopted by colliers in search of coal

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 which occurs in the same Coal Measures strata. The Farewell Rock has itself been worked for the production of refractory

Refractory

A refractory material is one that retains its strength at high temperatures. ASTM C71 defines refractories as "non-metallic materials having those chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above...

bricks, the high purity of the sandstone (over 98% silica) being suitable for this purpose.