In India, coal occurs in rock series of two main geological ages. The
Gondwana coal was formed over 200 million years ago. The tertiary
deposits are about 55 million years old. The major sources of Gondwana
coal are located in the Damodar valley (West Bengal-Jharkhan). In this
belt, Jharia, Raniganj and Bokaro are important coalfields. Coal
deposits are also present in the Godavari, Mahanadi, Son and Wardha
valleys. Tertiary coal is found in the north-eastern states of
Meghalaya, Assam, Arunachal Pradesh and Nagaland.