This section is from the book "The Law Of Real Property and Other Interests In Land", by Herbert Thorn Dike Tiffany. Also available from Amazon: A Treatise on the Modern Law of Real Property and Other Interests in Land .
Applying the considerations above recited, in connection with the general principle that a limitation of an estate of freehold to commence in the future will he regarded as creating an executory interest only when it cannot he regarded as creating a contingent remainder, it follows that an executory interest of a freehold nature may exist in the following cases: (1) When no actual estate is created by a previous limitation in the same instrument, as in the simple case of a gift to A and his heirs from and after A's marriage. (2) When an actual estate is created by the same instrument, but the vesting cannot occur until the lapse of an interval after the expiration of such estate, as in the case of a gift to A for life and, one day after A's death, to B and his heirs. (3) When an actual estate is created by the same instrument, and the vesting must or may occur before the expiration of such estate, and an intention appears that the vesting shall operate to divest such estate; as in the case of a gift to A and his heirs, or to A for life, but if B marries then to B and his heirs. (4) When an estate for years is created by the same instrument, and the vesting may occur before its termination, but no intention appears that the estate for years shall thereupon be divested, as in the case of a gift to A for ten years, and after that time to B and his heirs provided B marries.54 (5) Conceding the existence of determinable fees,55 when such a fee is created, and there is also limited by the same instrua vested remainder. Gray, Perpetuities, Sec. 114, note 2.
53. 2 Preston, Abstracts, 172; 1 Jarman, Wills, 835. Ante Sec.Sec. 161,
54. Post Sec. 173, notes 35-40.
55. Ante Sec. 90.