intercalation

n. [ L. intercalatio: cf. F. intercalation. ] [ 1913 Webster ]

1. (Chron.) The insertion of a day, or other portion of time, in a calendar. [ 1913 Webster ]

2. The insertion or introduction of anything among others, as the insertion of a phrase, line, or verse in a metrical composition; specif. (Geol.), the intrusion of a bed or layer between other layers. [ 1913 Webster ]

Intercalations of fresh-water species in some localities. Mantell. [ 1913 Webster ]