A.B.N.Sinha, J.

1. Except In C. W. J. C. No. 1146 of 1968, in all the rest of these applications under Article 226 of the Constitution of India, common questions of law arise for determination. Broadly speaking, the questions relate to the vires, true scope and construction of Sec.30A of the Mines and Minerals (Regulation and Development) Act 1957, (hereinafter referred to as the "1957 Act"). In all these cases the petitioners are holders of mining leases, either under a head-lease or under a sub-lease in respect of coal and have obtained a rule nisi calling upon the respondents to show cause why the demand through relevant letters and notices or certificate cases in respect thereof for royalty at the rate of five per cent. F. O. R, price of coal, less such amount as might have been paid already, in respect of coal removed by them as lessees or sub-lessees, either during the period 3rd November 1951 to the 31st December, 1965, or during the period the 29th December, 1961 to the 31st December, 1965, be not quashed as wholly illegal and appropriate writs or orders be not issued in that connection. In two cases only, namely, C. W. J. C. Nos. 1101 and 1194 of 1968, the period i