(GK) THE WORLD : The Lithosphere

GK : THE WORLD

The Lithosphere:
The mass of the Earth is generally divided into three layers, namely, Crust, Mantle and Core. The Lithosphere is the name given to the outer Crust which is not more than 10 miles thick. It is made up of a great variety of rocks, soils, etc.

Rocks:
1. Sedimentary Rocks:These rocks are made up of deposits laid down on the floor of river beds, lakes and seas. Examples:Sand and sandstone, clay, lime stone, chalk and carbonaceous rocks, such as lignite, coal and anthracite.

2. Igneous Rocks:These are primary rocks which are formed by cooling and solidification of molten lava. When such rocks are poured out on the surface they are known as Volcanic rocks, e.g. basalt. When the molten material solidifies at considerable depth, plutonic rocks are formed, e.g. granite. 

3. Metamorphic Rocks:These rocks are formed as a result of alteration by extreme heat and or pressure of igneous or sedimentary rocks. Example, slate, gneiss, schist etc.

Soil:
The upper layers of rocks weather to form the soil. There are three distinct layers of soil. The uppermost layer forms the top soil. The second layer is called the subsoil. The third layer is made up of decomposing and much-broken rock, known as mantle- rock. The type of soil depends on a number of factors, namely, climatic conditions, the nature of the parent rock, relief, vegetation and the period over which it has been worked by man. Soils may by broadly classified as (a) Forest, (b) Grassland and (c) Desert types.

Mountains:
In past geological ages disturbances in the Earth’s interior have caused crumpling and cracking of the crust. This has resulted in great upholds forming Fold- Mountains which are mainly made up of folded strata of sedimentary rocks, e.g. the Alps, the Rockies, the Andes, and the Himalayas. The mountain structures worn down by prolonged denudation are known as Residual Mountains, e.g. Highlands of Scotland and Scandinavia.

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