Old Red Sandstone

Old Red Sandstone, often called ORS, is a special group of rocks found in many places around the North Atlantic Ocean. These rocks are mostly from a very old time called the Devonian period. You can find them in eastern parts of Great Britain, Ireland, and Norway, and also along the east coast of North America. They even stretch up into Greenland and Svalbard.

These rocks were once part of a huge, ancient land called Euramerica. In Britain, scientists call this group of rocks a "supergroup" because it is very important for studying very old fossils. The word "Old" in its name helps to tell it apart from another group of rocks called the New Red Sandstone, which is younger and also found in many parts of Britain.

Sedimentology

The Old Red Sandstone is a group of sedimentary rocks formed in different places during the late Silurian, through the Devonian and into the early Carboniferous periods. These rocks are mostly made from pieces of land and conglomerates, and later include materials from dunes, lakes, rivers, and coastal areas. Though once believed to form only in freshwater, we now know some parts were laid down near the sea, as shown by fossils and studies of the rocks.

The red color of these rocks comes from iron oxide, but they aren't all red sandstones. They also include conglomerates, mudstones, siltstones, and thin limestones, showing colors from grey and green to red and purple. These deposits are linked to the erosion of the Caledonian Mountains, formed when the ancient continents of Avalonia, Baltica, and Laurentia collided.

Many fossils, such as early fishes, arthropods, and plants, are found in these rocks. While most of the rock does not contain fossils, some layers do have them. Similar-aged rocks in South West England are of true marine origin and are not part of the Old Red Sandstone.

Stratigraphy

Since the Old Red Sandstone is made mostly of rocks from land, it does not usually contain fossils from the sea. This makes it hard to match different places where these rocks are found. Because of this, scientists gave special names to the different layers of rocks in each area. These names are still used sometimes, but now more people use international names.

The Old Red Sandstone is found in many different areas called basins. One big basin is in North East Scotland and nearby seas. It covers places like the Moray Firth, Caithness, Orkney, and Shetland. In some parts of Shetland, these rocks are more than four kilometres thick. Another area with these rocks is around Oban and the Isle of Kerrera on the west coast of Scotland. These rocks are mostly from the late Silurian to early Devonian time and include sandstones, mudstones, and some fossils, especially fish.

There are also many places in the Midland Valley of Scotland where these rocks are found, along with some volcanic rocks. In the Scottish borders, there are outcrops from East Lothian to Berwickshire. A famous spot there is Siccar Point, where an old rock layer sits on top of much older rocks. The Anglo-Welsh Basin stretches across South Wales, from Pembrokeshire through places like Carmarthenshire, Powys, and Monmouthshire, and into parts of England like Herefordshire, Worcestershire, and Gloucestershire. In Pembrokeshire, the layers of rocks are a bit different, with some middle layers missing in certain areas. In Anglesey, there is a small separate area with these rocks, mostly from the lower part, and they include both river and lake deposits.

History of study

In 1787, a scientist named James Hutton noticed something interesting near Jedburgh. He saw layers of very old rock sitting on top of much older rock at Inchbonny. Later, he and a friend, John Playfair, went to the coast near Berwickshire and found more examples near Cockburnspath. They even took a boat trip with another scientist, Sir James Hall, and saw a clear example at Siccar Point, where layers of Old Red Sandstone sat on top of even older rocks.

During the early 1800s, several scientists studied these rocks closely. One of them, Adam Sedgwick, figured out that these rocks belonged to a time period we now call the Devonian. The name "Old Red Sandstone" was first used in 1821 by a Scottish scientist named Robert Jameson to describe these red rocks. Back then, people thought these rocks were similar to some rocks in Germany, but we now know they formed around the same time in different places.

Use as a building stone

The Old Red Sandstone has been used a lot for building in many places where it is found. You can see it in buildings near Stirling, Stonehaven, Perth, and Tayside. People in Caithness in Scotland also used this stone a lot. It was also used in places like Herefordshire, Monmouthshire, and old Brecknockshire in Wales.

Notable buildings

Canada

• New York Life Insurance Building, Montreal

England

• Goodrich Castle, Herefordshire
• Ross-on-Wye market hall, Herefordshire
• Shrewsbury Castle, Shropshire
• Hereford Cathedral, Herefordshire
• St. Mary Magdalene church, Taunton, Somerset

Scotland

• Arbroath Abbey, Angus
• Balvaird Castle, Perthshire
• Muchalls Castle, Aberdeenshire
• St Magnus Cathedral, Orkney
• Stonehaven Tolbooth, Aberdeenshire

Wales

• Raglan Castle, Monmouthshire
• Tintern Abbey, Monmouthshire
• Brecon Cathedral, Powys