And be it further enacted, That where any new Edifice or Building shall be erected or agreed to be erected on Ground belonging to the Grown, within the ordering and Survey of the Chancellor and Council of the Duchy of Lancaster, or of the said Surveyor General aforesaid, or held under any Lease from the Grown, for the Enlargement of, and to be united to and, occupied with any House or other Building held under any other Lease from the Crown, it shall- be lawful to grant a new Lease or Leases for any Term not exceeding Ninety-nine Years, as well of the Ground on which such new Edifice or Building shall be erected or agreed to be erected, as of all or any Part of any other Tenements or Hereditaments contained in such Leases ; provided, that the greater Part of the yearly Value of the Tenements and Hereditaments so to be granted shall consist of the Buildings thereon, or of Ground set apart and appropriated for building, or for necessary Gardens, Yards, Curtilages, or other Appurtenances as aforesaid.