Sedimentary rocks were formed after the igneous rocks. Sedimentary rocks are formed by the accumulation of many types of materials and sediments. These rocks are formed by the accumulation of layers over the layers on the fossils of living – organism vegetation and rocks-flour of different rocks. 

These rocks are classified into the following parts:

Classification of Sedimentary Rocks: Sedimentary rocks are formed by many types of materials and sediments. 

These rocks are classified on the following basis:

1. On the basis of the sediments used in formation. 

2. On the basis of the resources used in formation.

1. On the basis of the sediments used in formation: In this classification of rocks, the rocks are classified into clastic rocks, Organically Formed Rocks and Chemically Formed Rocks.

(a) Clastic Rocks: Rocks – flour obtained by the processes of weathering and erosion gets accumulated at a place in the form of layers. Over the passage of time, this accumulation organizes and takes the form of sedimentary rocks. 

Examples: Sandstone, Clay, etc. 

(b) Organically Formed Rocks: Rocks which are formed by the fossils of living – organisms and vegetation are included in this category. This includes lime – oriented and carbon – oriented rocks. 

Examples: Dolomite and Coal – oriented rocks. 

(c) Chemically Formed Rocks: Rocks which are formed when various chemical substances dissolved and solidified are included in this category.

Examples: Alabaster, Gypsum, Sart rock, etc.

2. On the basis of the resources used in formation: On this basis, the sedimentary rocks are classified into three parts: Aqueous Rocks, Aeolian Rocks and Glacial Rocks.

(a) Aqueous Rocks: These rocks are formed by the deposition of sediments in aquatic parts. Like-river rock, sea rock, etc. 

(b) Aeolian Rocks: These rocks are formed by the transportation and deposition of particles by wind; e.g. Loess 

(c) Glacial Rocks: Rocks which are formed by the transportation and deposition of pebbles and boulders by the glaciers.