Rocky period of history? (5,3)
I believe the answer is:
stone age
'rocky period of history?' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stone age that I've seen before include "before copper came in" , "time long ago" , "Pre-historic era" , "Go, senate to ancient era before metal was discovered" , "Hard time" .)