Where it appears to an inspector that doubt exists with respect to the boundary between two adjoining quarries, he may, by notice served on the owner of the quarries in a case where the same person is owner of both quarries, or on the respective owners of the quarries in any other case, require that, before the expiration of such period as may be specified in the notice, the boundary between the two quarries shall be determined by the owner or, as the case may be, by agreement between the respective owners and as so determined shall be notified to the inspector for the district by written instrument lodged with him by the owner or owners; and the boundary as so notified in compliance with the requirements of the notice shall, subject to any subsequent variation so determined and notified, be deemed for the purposes of this Act to be the boundary between the two quarries.

In any proceedings taken in respect of the failure of the owner of one of two adjoining quarries who is not also the owner of the other quarry to comply with the requirements of a notice under the foregoing subsection, it shall be a defence to prove that the failure was solely due to his inability to reach agreement with respect to the boundary with the owner of the other quarry.