The Secretary of the Interior is authorized and empowered to grant a right-of-way in the nature of an easement for the construction, operation, and maintenance of pipe lines for the conveyance of oil and gas through any Indian reservation, through any lands held by an Indian tribe or nation in the former Indian Territory, through any lands reserved for an Indian agency or Indian school, or for other purpose in connection with the Indian Service, or through any lands which have been allotted in severalty to any individual Indian under any law or treaty, but which have not been conveyed to the allottee with full power of alienation upon the terms and conditions herein expressed. Before title to rights of way applied for hereunder shall vest, maps of definite location shall be filed with and approved by the Secretary of the Interior: Provided