An agreement for a lease or tack, or with respect to the letting of any lands, tenements, or heritable subjects for any term not exceeding thirty-five years, or for any indefinite term, is to be charged with the same duty as if it were an actual lease or tack made for the term and consideration mentioned in the agreement.

A lease or tack made subsequently to, and in conformity with, such an agreement duly stamped is to be charged with the duty of sixpence only.