Geography Ch02 – Geological Structure of India

🌍 Origin — Pangaea Theory

🌐 Division of Pangaea

Pangaea → divided into Angaraland (North) and Gondwanaland (South)
Indian subcontinent was part of Gondwanaland

📊 4 Groups of Indian Rocks

1️⃣

Archaean Group

2️⃣

Purana Group

3️⃣

Dravidian Group

4️⃣

Aryan Group

⏳ Geological Timeline

Era-wise Classification

Oldest

Archaean / Pre-Cambrian Era

Gneiss & Schist — No fossils — 86.7% of Earth formation

Purana Group

Cuddapah + Vindhyan Systems

Layered sedimentary rocks — Origin of life — Eastern Ghats, Vindhya Plateau

Paleozoic Era

Dravidian Group

First evidence of life — Rich fossils — Absent almost everywhere except Rewa (MP)

Mesozoic → Recent

Aryan Group

Gondwana (coal), Deccan Trap (basalt/black soil), Tertiary (Himalayas), Quaternary (alluvial)

⚡ QUICK RECALL — Fossil Memory

Archaean → No fossils (Earth cooling)
Dharwar → No fossils
Cuddapah → No fossils (origin of life only)
Vindhyan → General absence of fossils
Dravidian → RICH fossils (first life evidence) ✅
Gondwana → Fossils present ✅

⛏️ Group 1 — Archaean

🌏 Archaean System — Most Ancient Rocks

Contribute ~86.7% in formation of the Earth
Formed during cooling of the Earth
No Fossils — Pre-biological era
Rock types: Gneiss and Schist

Bundelkhand Gneiss (most ancient)

Bengal Gneiss

Found In:

Karnataka

Tamil Nadu

Andhra Pradesh

Madhya Pradesh

Odisha

Chotanagpur Plateau (Jharkhand)

🏔️ Dharwar System of Rocks

Formed by erosion & deposition of Archaean rocks
Most developed in Dharwar region, Karnataka
No Fossils
Aravalli mountain range — formed from these rocks

⚡ QUICK RECALL

Dharwar rocks → Aravalli mountainsformed | Most developed inKarnataka (Dharwar district)

🚨 EXAM TRAP

Bundelkhand Gneiss = most ancient rocks of India
Archaean rocks represent the earliest and most extensive phase of Earth's crustal formation described here, accounting for 86.7%.
The Aravalli system is associated with Dharwar rocks rather than the older Archaean system in this classification.

📦 Group 2 — Purana

🔵 Cuddapah System

Formed by erosion of Archaean + Dharwar rocks
Layered rocks (sedimentary)
No fossils — but origin of life on Earth
Named after Cuddapah district, Andhra Pradesh
Eastern Ghats — formed from these rocks

🟣 Vindhyan System

Plateau — divides Ganga Plain from Deccan
Layered, formed by water deposition
General absence of fossils
Minerals: limestone, sandstone, china clay, copper clay

📊 Cuddapah vs Vindhyan — Comparison

Feature	Cuddapah System	Vindhyan System
Formation	Archaean + Dharwar erosion	Water deposition
Fossils	Absent (origin of life)	Generally absent
Landform	Eastern Ghats	Vindhya Plateau
Named After	Cuddapah district (AP)	Vindhya mountains
Minerals	—	Limestone, Sandstone, Clays

🚨 EXAM TRAP

The Eastern Ghats are associated with the Cuddapah rock system.
The Vindhyan range forms an important divide between the Ganga Plain and the Deccan region.
The Cuddapah system is named after the Cuddapah region of Andhra Pradesh, where these rocks are extensively found.

🦕 Group 3 — Dravidian

🦴 Paleozoic Era Rocks

Rocks of Paleozoic Era
First evidence of life on Earth
This rock system is especially rich in fossils.
Absent from almost whole India
Found only in: Rewa district, Madhya Pradesh

🚨 EXAM TRAP — Most Asked!

Dravidian Group = almost absent from India— onlyRewa (MP)are found in. but most important =First/Rich Fossils. this contradiction remember!

⚡ QUICK RECALL

Dravidian = Paleozoic Era | Rich Fossils = First life evidence | Location = Only Rewa, MP

🔥 Group 4 — Aryan (4 Sub-Systems)

🪨 1. Gondwana System — Coal Treasure

Construction of basin landforms
Fossils present
~98% of India's coal reserves found here!

Spread In:

Damodar Valley

Mahanadi Valley

Rajmahal

Satpura

98%

India's Coal Reserves in Gondwana Rocks

🌋 2. Deccan Trap System — Black Soil Origin

End of Cretaceous Era → Volcanic activity in western Peninsular India
Basalt lava flow → step-like landform (trap = step)
Mainly in Maharashtra and Malwa region
Also formed: Rajmahal Trap
Basalt erosion → Fertile Black Soil (Regur)

Deccan Trap States:

Maharashtra

Gujarat

Karnataka

Andhra Pradesh

⚡ QUICK RECALL

Deccan Trap → Basalt Lava → Black Soil (Regur/Cotton Soil) → Best for cotton cultivation

🏔️ 3. Tertiary System

Formed: Eocene to Pliocene epoch
Formation of Peninsular Plateau
Formation of Himalayan mountains

🌊 4. Quaternary System

Rocks of Pleistocene + Holocene epoch
Deposits at mouths of Indo-Gangetic Plains
Also in Deltaic regions
Most recent rocks

🚨 EXAM TRAP

About 98% of India's coal resources occur in Gondwana rock formations.
Black soil developed from Deccan Trap basalt, not from Gondwana rocks.
"Trap" word comes from Swedish "trappa" = stairs/steps — step-like lava landform
The Damodar Valley is a major Gondwana coal belt extending through the Jharkhand–West Bengal region and is important for eastern India studies.

📋 Complete Master Summary Table

Group	System	Era	Fossils	Key Feature	Location/Landform
1. Archaean	Archaean System	Pre-Cambrian	Absent	86.7% Earth formation, Gneiss & Schist	Karnataka, TN, AP, MP, Odisha, Jharkhand
1. Archaean	Dharwar System	Pre-Cambrian	Absent	Formed from Archaean erosion	Aravalli mountains, Dharwar (Karnataka)
2. Purana	Cuddapah System	Pre-Cambrian	Absent	Origin of life, layered rocks	Eastern Ghats, Cuddapah (AP)
2. Purana	Vindhyan System	Pre-Cambrian	Gen. Absent	Limestone, Sandstone, Clays	Vindhya Plateau (Ganga–Deccan divide)
3. Dravidian	Paleozoic Rocks	Paleozoic	Rich Fossils	First life evidence, Absent almost everywhere	Only Rewa district (MP)
4. Aryan	Gondwana System	Mesozoic	Present	98% India's coal reserves	Damodar Valley, Mahanadi, Rajmahal, Satpura
	Deccan Trap	Cretaceous end	—	Basalt lava → Black Soil (Regur)	Maharashtra, MP, Gujarat, Karnataka, AP
	Tertiary System	Eocene–Pliocene	—	Himalayas + Peninsular Plateau formed	Himalayan region
	Quaternary System	Pleistocene–Holocene	—	Most recent rocks	Indo-Gangetic Plains, Delta regions

🎯 Most Important Points for BPSC/BSSC

🚨 Top Exam Points

Coal (98%) → Gondwana rocks
Black Soil → Deccan Trap (Basalt)
Richest fossils → Dravidian Group
Dravidian rocks in India → only Rewa (MP)
Aravalli → Dharwar rocks
Eastern Ghats → Cuddapah rocks
Most ancient → Bundelkhand Gneiss
IST + Tropic of Cancer meet → Chhattisgarh

⚡ Memory Tricks

A P D A = Archaean, Purana, Dravidian, Aryan (4 groups order)
No fossils → Arch, Dhar, Cudd, Vindh (4 oldest)
Gondwana = Coal = Damodar Valley (JH/Bihar)
In Deccan Trap, the term trap refers to the step-like landform produced by successive basaltic lava flows.
Quaternary = most RECENT → alluvial soil of Ganga

⚡ BIHAR SPECIAL RECALL

The Gondwana coalfields of the Damodar Valley lie along the Jharkhand–West Bengal belt, close to Bihar.
Chotanagpur Plateau (Jharkhand) = Archaean rocks — mineral rich area
The Indo-Gangetic Plain, including the Bihar Plain, consists largely of fertile Quaternary alluvial deposits.

🪨 Indian Geography — Chapter 02