7 In the cases of the preceding two paragraphs, the works of the salt-fields, etc. where the damaged places lie in succession at intervals within fifty metres, and the works of the saltfields, etc. where the damaged places lie in succession at intervals exceeding fifty metres for which the separate working is difficult or inappropriate in view of the use of the salt-fields, etc., shall be deemed to be one lot of the works provided that this shall not apply to the case where there are two or more persons carrying out the works concerned.