Before voting on the enactment of an amendment, the Board of Supervisors shall hold a public hearing thereon, pursuant to public notice. In the case of an amendment other than that prepared by the Planning Commission, the Board of Supervisors shall submit each such amendment to the Planning Commission at least 30 days prior to the hearing on such proposed amendment to provide the Commission an opportunity to submit recommendations. If, after any public hearing held upon an amendment, the proposed amendment is revised or further revised to include land previously not affected by it, the Board of Supervisors shall hold another public hearing, pursuant to public notice, before proceeding to vote on the amendment.