Periodically fancy that series of old deeds (4)
I believe the answer is:
Here is my best explanation:
'series of old deeds' is the definition.
(historic term for a collection of records)
'periodically fancy that' is the subsidiary indication.
'periodically' indicates alternate letters (letters must be selected 'every so often').
The alternate letters of 'fancythat' are 'acta'.
(Other definitions for acta that I've seen before include "records", "Minutes", "minutes of official proceedings" and "Official minutes".)