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Rocks

Sedimentary Rocks - Transport and Compaction.

Small pieces of weathered rock (sediments) are transported by rivers.
This means that the rock pieces are moved along
as the river flows towards the sea.

During transportation, the sediments are sorted according to size.
The largest pieces tend to be deposited first.
Sand is next to settle out of the water. The smallest particles are mud or clay,
and these are moved furthest by the river and deposited last.

With the passing of time, the deposits of sediment get thicker and thicker.
Sediment underneath becomes increasingly crushed
by the weight of new sediment above. This is called compaction.

It is this process of compaction
which eventually gives rise to the sedimentary rock.
The process may take millions of years.
The largest rock pieces will produce conglomerate.
Sand will produce sandstone.
Mud or clay will produce mudstone or shale.

Younger sedimentary rocks are usually found on top of older rocks.
Rock layers generally get older the deeper down you go.

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Copyright © 2008 Dr. Colin France. All Rights Reserved.