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Imperial Gazetteer of India, v. 1, p. xv.

TABLE OF CONTENTS xv PAGE Comparative uniformity of life in the ocean 52 Want of strict contemporaneity in geological formation 52 Use of local stratigraphical names . . . . . 52 Classification of Indian strata . . . . . . 53 The datum line in stratigraphy. . . . . 53 The Olenellus zone . . . . . . . 53 Pre-Cambrian unfossiliferous rocks . . . 54 Fossiliferous deposits . . . . . . 54 Four resultant main groups . . . . . . 54 Archaean group . . . . . . . . 54 Purana group . . . . . . . . 54 Grouping of the fossiliferous strata . 56 The Upper Palaeozoic break . 56 Dravidian and Aryan groups . . . . 56 The Dravidian group in extra-peninsular India. 57 Fresh-water deposits in the Aryan group . 57 Marine deposits in the Aryan group 57 II. Pre-Cambrian Hislory of India The Archaean and Purina eras in the pre-Cambrian history of India . . . . . . . 57 The great Eparchaean break . 58 Archaean era . . . . 58 Area of the Archaean rocks . . . 58 Origin and nature of the fundamental complex. 58 Orthogneisses and paragneisses 59 Mixed gneisses . . . . . . . . 59 Chief divisions of the Archaean group 59 The Dharwarian system . . . . . . . 60 The Purana era . . . . . . . . Distribution of the Purana group 6. . . . . Lower and upper divisions of the Purana group 6. . The Cuddapah and Kurnool systems 6. . . . The Vindhyan system 62 The Purana group in Burma . 62 Possible existence of the Purana group in the Himalayas . 63 III. Cambrian and Post-Cambrian History of India A. The JDravidian Era The Cambrian of the Salt Range 64 Purple sandstone and Neobolus beds 64 Magnesian sandstone series and salt pseudomorph zone 65 Palaeozoic of the Central Himalayas . 65