Intercalation
Intercalation , noun
[Latin intercalatio: compare French intercalation.]
1.
(Chron.) The insertion of a day, or other portion of time, in a calendar.
2.
(Geology) The insertion or introduction of anything among others, as the insertion of a phrase, line, or verse in a metrical composition;
(Geology) the intrusion of a bed or layer between other layers.
Intercalations of fresh-water species in some localities.