The present physical form of the Indian subcontinent is the result of a vast geological formation. India is mainly composed of three geological units: (a) the peninsular plateaus, (b) the Himalayan mountains, and (c~ the Indo Gangetic plains. Most of the geologists believe that the Indian peninsula, the oldest of the three geological forma tions, was a part of the global Gondwanaland (continent), which drifted northwards and striking with the Central Asiatic plates raised up to form the high Himalayas out of the Tethys sea.
Geological’ formations of India may be divided into four groups: (i) the Archean (the earliest), (ii) the Purana, (iii) the Dravidian and (iv) the Aryan (the youngest). The Archean of India corresponds to the first half of the Pre Cambrian era, and the Pur ana to the second half of the Pre-Cambrian. The Dravidian covers the period from Cambrian to middle Carboniferous, while the Aryan from the Carboniferous to the Pleistocene (see table on major geological formations of India).
INDIAN ROCK SYSTEMS AND THEIR OCCURRENCE Important Indian rock systems and their characteristics are listed as under:
(i) The Archean System contains the first formed rocks of the earth. These rocks in the peninsula are found primarily in Tamil Nadu, Andhra Pradesh, Chhattisgarh, Jharkhand and Rajasthan. The rocks are primarily gneisses and granites, having no marks of fossils.
(ii) The Dharwar System of rocks are the earliest formed sedimentary rocks, found today in metamorphic forms. These rocks do not contain fossils and are found in Karnataka, Madhya Pradesh, Jharkhand, Meghalaya and Rajasthan. They occur also in the central and northern Himalayas. Schists, slates, quartzites and conglomerates are some of the rocks. This system carries minerals like gold, manganese ore, iron ore, chromium, copper, uranium, thorium, mica and building materials like granites, marbles, quartzites and slates.
(ill) The Cuddapah System of rocks are found in Rajasthan, Tamil Nadu, Andhra Pradesh, Madhya Pradesh and Chhattisgarh. These rocks contain iron ore, manganese, ore slate and marble.
(iv) The Vindhyan System of rocks stand over the
Cuddapah rocks and cover large areas in Madhya Pradesh, Chhattisgarh, Uttar Pradesh and Rajasthan. This system contains rocks like limestones, sandstones, shales and slates which are useful as building materials.
(v) Gondwana System of rocks contain coal deposits and have marks of climatic changes from arctic cold to tropical and desert conditions. These rocks are found mainly in the Damodar, the Mahanadi and the Godavari val leys of the peninsula.
(vi) The Deccan Traps Sys tem of rocks, volcanic in nature, are found in Maharashtra and other parts of the Deccan. These volcanic rocks also contain some thin fossiliferous sedimentary layers found between the lava flows. The volcanic activity in the region led to two great events: (i) break up of the Gondwana landmass, and (ii) uplift of the Himalayas out of the Tethys sea.
(vii) The Tertiary System of rocks are found mostly in the Himalayas. In the peninsula, they occur in coastal areas of Gujarat, Kerala and Tamil Nadu. The Ter
tiary rocks contain brown coal, rock salt, gypsum and limestone.
(viii) Quaternary System The
important quarternary forma
tions are Ice Age deposits in Kash mir, formation of alluvial plains in north India, creation of Rajasthan deserts, Rann of Kachchh, laterite