WBBSE Class 7 Geography Chapter 6 Rock And Soil Introduction
A mineral is a naturally-occurring inorganic substance that consists of one or more elements to form a rock. Rock are naturally formed aggregates made up of one or more minerals. In other words, all components that made up the Earth’s solid crust are called rocks.
For millions of years, various natural forces have acted on the rocks. As a result disintegrated finer particles are formed. These are called regolith. This regolith mixes with organic matter (formed by the decomposition of dead plants and animals) and forms a thin and soft layer, which is conducive to plant growth, on the Earth’s crust. This layer is called soil.
Volcanic eruptions of magma accumulate on the Earth’s surface or beneath the Earth’s surface and then gradually cool down and harden to form igneous rocks. The igneous rocks get disintegrated by the action of different natural agents and are subsequently deposited in layers on the sea bed.
Read And Learn Also WBBSE Class 7 Geography Notes
With the passage of time, after being subjected to high pressure and temperature, these layers of sediments undergo solidification to form hard rocks called sedimentary rocks. Under high temperatures and great pressure, a pre-existing igneous or sedimentary rock may change into a new form which is of rock called metamorphic rock. These rocks are hard and resistant to erosion.
The soil that contains a high amount of sand and is not suitable for agriculture is called sandy soil. The soil that contains an equal amount of sand and silt and a little amount of clay and is ideal for agriculture is known as loamy soil. The soil that has a high amount of clay particles and has high water-holding capacity is known as clayey soil.
For millions of years, various physical, chemical and organic processes have acted on the rocks thereby disintegrating them into smaller fragments. These fragments after that formed a loose, unconsolidated layer on the Earth’s surface called regolith. Soil is actually formed from regolith.