sedimentary rocks

how was it formed

• formed over millions of years on land, lake beds or beneath the sea

• two types of sedimentary rocks: organic and inorganic

limestone

• organic sedimentary rock - formed from the remains of animals and plants

• most common rock in ireland

• Found in Burren Co. Clare - well known for limestone region

• can also be found under soil and bogs of the central plain

how is it made

• made from cemented and compressed remains of fish and sea creatures - built on top of each other

• over millions of years they compressed each layer and formed solid rock

• Limestone contains calcium carbonate - comes from calcium in bones of sea creatures

• vary in colour

exposed limestone

• formed approximately 350 MYA when ireland was close to the equator

• this type of limestone was formed - carboniferous period - called Carboniferous limestone

sandstone

• an inorganic sedimentary rock - formed from broken-down remains of pre-existing rock

• can be found in Comeragh mountains in county waterford and Macgillycuddy Reeks in Co.Kerry

appearance of sandstone

• a coarse grained rock, usually brown or red in colour

• common rock in ireland is old red sandstone - red colour comes from iron oxide

old red sandstone

• formed 400 MYA - Ireland had a desert-like climate - due to its position

• during this time, Caledonian fold mountains were being weathered and eroded

formation of sandstone

• sediments were carried by rivers which deposited them in lakes

• sediments laid in layers - strata

• over time the - layers compressed to the next - layers of sand were cemented to form sandstone

• Sandstone is also formed when deposits of sediments were layed down in river channels, deltas and flood plains