Any territory contained within a district not being served by any transit facilities of the district and not included within the boundaries of any incorporated city and not benefited in any manner by the district or by its continued inclusion therein may be excluded therefrom by order of the board upon the verified petition of the owners in fee of lands whose assessed value with improvements is in excess of one-half of the assessed value of all the lands with improvements held in private ownership in the territory sought to be excluded.