Section 30. They shall commit or bind over for trial in the superior court persons brought before them who appear to be guilty of crimes not within their final jurisdiction, and may so commit or bind over persons brought before them who appear to be guilty of crimes within their final jurisdiction. If such a person is committed for failure to recognize as ordered, the superior court shall thereupon have jurisdiction of the case against such person for the purpose of revising the amount of bail theretofore fixed.