When some of the lands forming the estate are held in common, the Collector shall declare, by a proceeding to be held under the provisions of this Act, the principle and rule under which, in accordance with the village custom, such lands shall be divided;
     and he shall cause the partition of such lands to be made in conformity to the provisions of this Act.
     The portion of the common land falling by such partition to the shares of the several co-sharers shall be added to the lands held by them in severalty, and the several estates thus formed shall be assessed and declared separate estates.
     Proviso.--Provided that it shall be in the discretion of the Collector to cause any transfer of lands, agreed to by the parties, to be made previous to such declaration, and the new estate shall be declared subject to the transfer so made.