59 C.J.S. Mortgages § 218, p. 287. The general rule is quoted in McBride v. McBride, 152 Or. 601, 54 P.2d 838, 841, as follows: "The parties may, as between themselves, make a valid agreement, though it be verbal only, that one of two mortgages shall be prior to the other, and the order of record is then immaterial unless they are subsequently assigned to other persons who have no notice of the agreement. * * *"