3.1.2. Sedimentary Rocks

The word sedimentary has been derived from the Latin word ‘sedimentum’, meaning settling

down.

Rain, wind, ice, running water, plants and animals constantly break the rocks into fragments of all sizes. These broken rock materials are carried away by wind, ice and running water, and deposited in the depressions. The deposited materials are called sediments, and they give rise to sedimentary rocks.

The sediments are generally deposited in horizontal layers or stratas. Thus these rocks are also referred to as stratified rocks. The loose materials are converted into hard and compact rocks such as shale and sandstone. This is due to the pressure exerted from the top or because of cementation.

The sedimentary rocks can be formed mechanically (sandstone), chemically (gypsum or salt) or organically (coal, limestone). The sedimentary rocks are most widespread and cover about 75 per cent of the total land area on the earth.