Download Rock type 1: Greywacke This rock is one of the most

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Rock type 1: Greywacke
This rock is one of the most common rocks found in NZ and makes up the main mountain chains
in both Islands. Greywacke is named because of its drab grey colour. It is a very hard sandstone
and forms huge thicknesses of sediment that have been uplifted by plate tectonics. Sandstone is
made from broken rock fragments that have been eroded and transported and eventually
dumped out at sea. Greywacke is made when all the sand is compressed by being buried deeply
in the Earth’s crust. Moving tectonic plates causes the pile of sediments to be pushed up and in
some cases to be pulled down.
Rock type 2: Limestone:
Limestone is made of shells and forms in shallow warm water. So, when the limestone was
made, the sea must have covered the land and as animals died their shells built up on the sea
floor. Limestone is made of calcium carbonate and is usually white or yellow in colour.
Sometimes it has sharks teeth in it and sometimes whole shells. The lime is made into limestone
when it becomes buried and compressed. Because the giant tectonic plates are constantly
moving, they sometimes cause the land to go up and down. As the land goes down, the sea is
able to cover the former land and deposits of lime can be formed.
Erosion and landforms.
When acid eats away limestone rock, it forms caves and caverns. Often the caves form because
they are eaten away from beneath and the bottom falls out. Sometimes the top is eaten away
and the ground sinks to be seen as sinkholes. These can be dangerous. In our local area, there
are many sinkholes and they often have underground streams in them that also erode the rock
away and carry the pieces down to the sea. These sinkholes often collapse above the direction of
flow of underground streams.