Which one among the following statements regarding India's coal is not correct? [CDS 2012] (a) 98 percent of reserves of coal in India belongs to Gondwana period (b) Unknown amount of coal lies buried under the Ganga alluvium and the Deccan Trap (c) Bituminous coal is found in both lower Gondwana rocks and in Tertiary rocks (d) Gondwana coal is mainly found in the river valleys of Damodar, Mahanadi and Godavari