Brewer's: Saturnian Days
Days of dulness, when everything is venal.
Then rose the seed of Chaos and of Night To blot oat order and extinguish light, Of dull and venal a new world to mould, And bring Saturnian days of lead and gold.
They are lead to indicate dulness, and gold to indicate venality.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894