13. Where notices vary---If a notice and cross-notice have been duly
 served or if notices to do work have been duly served and the proposals
 in those notices do not correspond, then (unless within 21 days after
 the date of the service of the last notice or cross-notice the
 differences are resolved by agreement) the matters in dispute may be
 determined by the Court in manner hereafter provided in this Act.
     Cf. 1908, No. 61, s. 14