The Coal Mines National industrial Board shall be dissolved; and accordingly the following provisions of the [20 & 21 Geo. 5. c. 34.] Coal Mines Act, 1930, are hereby repealed, namely, Part IV, subsection (1) of section sixteen and, in the definition of " coal mine " in subsection (1) of section eighteen, the words " (including for the purposes of Part IV of this Act lignite or brown coal) ".