Soil is the uppermost layer of the earth’s crust. It contains a mixture of fine powdered rock material and humus. Humus is the organic matter which is added to the soil by the decayed and decomposed remains of plants and animals.
Down to a depth of 16 km from the surface of land, 95 per cent of the earth materials found in the earth’s crust consist of rocks. Rocks are made up of individual substances, called minerals, found mostly in solid state.
Earth’s axis is an imaginary line which runs right across and passes through the centre of the earth. The earth spins round its axis which always remains inclined at an angle of 661/2° to the plane of the Earth’s orbit.
Vegetation comprises of plants growing over the surface of the earth. The plant geographers have divided the vegetation of the world into four great biochores :
The Forest Biochore : Defined as plant formation consisting of trees growing close together nd forming a layer of foliage that shades the ground.