The Jurisdiction of the said Great and Small Barmote Courts and of this Act shall be held to extend over the whole of the before-mentioned District called the King’s Field, and also over all the Parts of the Hundred of High Peak aforesaid in which Her Majesty in right of Her Duchy of Lancaster is entitled to the Mineral Duties, and the Mineral Laws and Customs of that Part of the said Hundred over which the Jurisdiction of the said Great and Small Barmote Courts is hereby declared to extend shall be such as are mentioned and comprised in this Act, and no other alleged Custom or Practice shall be valid.