Old Red Sandstone facts for kids
The Old Red Sandstone is a special type of dark red sandstone rock. It was formed a very long time ago, mostly during the Devonian period. This rock covers a huge area that was once a giant continent called Laurussia.
Laurussia is sometimes called the Old Red Continent. It included lands that are now parts of northern Europe, Greenland, and North America. Back then, this continent was located closer to the equator, between 0 and 30 degrees south.
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Discovering the Old Red Sandstone
The Old Red Sandstone (often called ORS) was first found in Great Britain. It played a big part in helping early scientists understand geology, which is the study of Earth's rocks and how they are formed.
The name 'Old Red Sandstone' was first used in 1821 by a Scottish scientist named Robert Jameson. He studied both nature and minerals.
In 1787, a famous Scottish geologist named James Hutton saw something amazing near Jedburgh in the Scottish Borders. This place is now known as Hutton's Unconformity. An unconformity is like a missing chapter in Earth's history book, where layers of rock don't line up perfectly because some time and rock layers are missing.
Later, Hutton found another important spot on the Berwickshire coast called Siccar Point. He described it as "a beautiful picture" where the sea had washed away the dirt to show the rock layers. Here, the 345-million-year-old Devonian Old Red Sandstone sits on top of much older, 425-million-year-old Silurian greywacke rock.
How the Rocks Were Formed
The unconformity at places like Siccar Point shows a big gap in Earth's geological record. During this time, the older rocks were pushed up above sea level. Then, erosion happened, which means wind and water wore them down. The rocks also bent and broke, a process called folding and faulting.
Huge mountains were formed when a part of northwestern Europe crashed into another large piece of land. This land was made up of parts of what are now North America and Greenland. This mountain-building event is called the Caledonian orogeny. The lower rock layers were tilted almost straight up!
After the mountains formed, the ORS rocks were laid down in low-lying areas called basins. These basins were like big valleys between the new mountain ranges. Rivers and lakes filled these basins. The ORS was formed in this non-marine (meaning not in the ocean) terrestrial (meaning on land) environment.
Over a very long time, thick layers of sand and mud collected in these basins. These layers could be as deep as 11,000 metres (about 36,000 feet)! They often looked red because of tiny iron minerals that had rusted.
The Old Red Sandstone was formed over a long period, from the very end of the Silurian period to the beginning of the Carboniferous period. This was roughly between 418 and 355 million years ago.
Different Kinds of Old Red Sandstone
The Old Red Sandstone is a rock formation that looks different depending on where you find it. This is because the conditions when it formed varied from place to place.
The dark red color of these rocks comes from iron oxide, which is like rust. However, not all Old Red Sandstone is red, and not all of it is sandstone! This rock group also includes other types of rocks like conglomerates (rocks made of pebbles), mudstones, siltstones, and thin layers of limestones. The colors can also range from grey and green to red and purple.
These rock deposits were made from sediment that came from the wearing down of the Caledonian Mountain chain. This mountain chain was created when the ancient continents collided to form the Old Red Sandstone Continent.
Images for kids
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Hutton's angular unconformity is at Siccar Point where 345 million year old Devonian Old Red Sandstone overlies 425 million year old Silurian greywacke.
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Siccar Point: eroded and gently sloping Devonian Old Red Sandstone layers cap over conglomerate layer and older vertically bedded Silurian greywacke rocks.
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St. Magnus Cathedral, Kirkwall, Orkney, built of local sandstone.
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The unconformity at Jedburgh: illustrated by John Clerk in 1787 with a recent photography by Keith Montgomery.
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St. Helen's Chapel at Siccar Point has walls faced in Old Red Sandstone, with greywacke used on the inner face and surrounding drystane dykes.
See also
In Spanish: Old Red Sandstone para niños
