Geological divisions of India
Topic: Structure and Physiography of India: Himalayas, Plains, Peninsula, Coasts and Islands · NCERT: Class 11, Ch 2 "Structure and Physiography"
Meaning
The geological divisions of India split the country by its rocks and how they formed, not by how the land looks. There are three: the Peninsular Block, the Himalayas and other Peninsular mountains, and the Indo-Ganga-Brahmaputra plain. The Peninsular Block is the oldest and most rigid part of India and is made mostly of ancient gneisses and granites. The Himalayas are young and still flexible, so faults, folds and thrusts (rock layers pushed up over others) keep forming. The plain began as a geosynclinal depression (a long, sinking trough), which rivers filled with 1,000-2,000 m of alluvium (river-laid silt and sand). These divisions explain where India's minerals, fertile soils and earthquake zones are.
Example
The Peninsular Block's northern edge runs from Kachchh along the western side of the Aravallis near Delhi, then roughly parallel to the Yamuna and Ganga, to the Rajmahal hills and the Ganga delta. Everything south of this line is old, stable rock rich in minerals.
Don't confuse with
- Physiographic divisions of India: there are six of these, and they group land by its relief (mountains, plains, plateau, desert, coasts, islands). The three geological divisions group it by structure and origin.