On the basis of stratigraphic, tectonic, and metamorphic studies in certain critical Pre-Cambrian areas of Nagpur-Bhandara-Drug region and twenty-six K-Ar age data of representative samples, the authors have suggested a new generalized succession and correlation of the dated orogenic cycles and phases, and have drawn the following conclusions:-(a) Amgaon cycle closed during the period 1444-1730 m.y. (6) Sakoli cycle (I phase) closed at 1330 m.y., and during Sausar orogeny (864-996 m.y.) the north-western part of Sakoli synclinorium was deformed and metamorphosed (862-950 m.y.). (c) Sausars and Sakolis, both post-Amgaon in age, were deposited in separate basins and had different tectonic histories.

Recent radiometric mineral dating carried out by K–Ar, Rb–Sr, and U–Th–Pb methods makes it possible to estimate the age boundaries for the main geological formations of the Baltic Shield.The relevant radiometric age zonation does not point to a zonation of continuous growth of the Baltic Shield from the center to the periphery. In its Precambrian history three main stages can be recognized. Most of this territory developed continuously from 3500 m.y. to 1650 m.y. ago. During this first, greatest period the main structural features of the Shield were formed.The following, Gothian period, corresponding to a time interval 1500–1000 m.y. was characterized by consolidation of the Shield and deposition of continental sediments. The main feature of the third, Riphean period beginning approximately at 1000 m.y. was the formation of the Sveco–Norwegian structural belt in the southwestern part of the Shield, discordant to the older formations.

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The procedure of mica age determination by the K‐A method is described. The age data obtained by the K‐A and Rb‐Sr methods for Precambrian of the USSR together with their estimation are given. The data obtained are compared with the stratigraphy.

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