Books of past and series of unremembered days (4)
I believe the answer is:
edda
'books of past' is the definition.
'edda' can be an answer for 'books' (I've seen this before). I am not certain of the 'of past' bit.
'series of unremembered days' is the wordplay.
'series of' says the answer is hidden in the clue (a series of letters from the clue).
'EDDA' is hidden within 'unremembered days'.
'and' is the link.
Can you help me to learn more?
(Other definitions for edda that I've seen before include "Ancient Icelandic writings" , "mythological book" , "Collection of myths" , "work in Scandinavia" , "Yarn" .)