Although erosion and later phases of tectonism tend to erase the past, we can still get some evidence of the past tectonic activities through study of rocks. From whatever idea we have, we can build tectonic framework of India and study each unit separately. The Himalayan mountain-building is relatively recent tectonic activity that India has experienced and because of this event we have broad three tectonic units which coincide with the three physiographic divisions - the Peninsula, the Extra Peninsula and the Indo-Gangetic Alluvial Plains.

The Extra Peninsula because of its uniqueness has been treated separately as Himalayan Geology. The Indo-Gangetic Alluvial Plains are mostly covered with recently deposited alluvium carried by two major river systems -- the Ganga and the Indus.

The Peninsula exhibits a geology that has not experienced any major deformation since the beginning of the Phanerozoic eon. The earliest rocks have been severely deformed during the Archaean and Proterozoic times. Eventually when they got stabilized, they formed basement for other rocks to be laid over them. We will study these earliest rocks under the heading Precambrian Basement. Precambrian Basement rocks are widespread in southern and south-eastern India and also in Aravalli Range of mountains.

Although there were phases of deformation in some parts during the Proterozoic, in some other places there had been quiet depositional activities during this time and these rocks still lie nearly flat covering large areas. We group such successions under Proterozoic Cover. Large basins with Proterozoic Cover rocks are exposed in north-central India and parts of Andhra Pradesh, Karnataka and Madhya Pradesh.

There were only occasional rock-building activities in Indian Peninsula after the close of the Precambrian. The central part remained above sea-level. Therefore, marine depositional activities are normally not to be expected there anymore. The Palaeozoic of Indian Peninsula therefore is represented by river deposits laid down in wide grabens. The deposition by ancient river systems continued until the end of the Mesozoic. These rocks are now exposed as Gondwana Supergroup in various modern river systems such as Damodar, Godavari, Mahanadi, Wardha and also in Satpura Hills of Madhya Pradesh.

Apart from the river deposits, the Mesozoic also witnessed a unique event in Indian history. Close to the end of Mesozoic, vast areas of western India were covered by lava flows identified as Deccan flood basalt. Similar lava flows were laid down in eastern India in Rajmahal Hills. Sedimentary deposition was confined to coastal areas which were occasionally flooded by the trangressing sea. Mesozoic and Cenozoic marine formations are found in coastal areas such as Kutch, Saurashtra, Jaisalmer, Assam-Arakan, Cauvery Basin.