When the limits of any mine join those of any other mine the companies respectively working the said mines may, with the consent in writing of the respective lessors thereof in all cases where such consent is by law or custom necessary, amalgamate and become one company, provided that no such amalgamation shall take place unless each of the said companies shall authorise the same by a special resolution, to which two thirds in value of the shareholders in the said company shall consent in writing; such resolution shall be registered in the court, and the amalgamation shall not take effect until such registration, and shall be advertised in such manner as the court directs.