GEOGRAPHY AND HISTORY

  Sedimentary rocks are rocks composed of deposited minerals and rock fragments or sediments produced by mechanical or physical or chemical weathering of former rock masses of igneous rocks. They have therefore derived from already existing igneous rocks and because of this, they are sometimes referred to as derived rocks or secondary or laid down rocks. The weathered materials are then transported by erosion agents of water, ice, and wind and are later deposited in layers (strata) on either a dry land or in valleys or under water (in oceans and seas). The layers are separated by bedding plains which demarcate the end of one deposition cycle and the beginning of another. Layers can be horizontal, gently sloping or steeply dipping. Generally speaking, sedimentary rocks have the following characteristics; They contain fossils of dead plants and animals. They have layers i.e. strata (they are stratified) They are non-crystalline in nature Stratas are either horizontal or gently slopin...