Time drives the flocks from field to fold (5)
The meter of "time drives" as a spondee foot forces the line on at a quicker pace, mirroring the imminent approach of winter. Brr!
When Rivers rage and Rocks grow cold,And Philomel becometh dumb; (6-7)
The phrasing of "rocks grow cold" is yet another mockery of the life Marlowe's shepherd sees in nature. By putting the words "rocks" and "grow" next to each other when everyone knows that rocks cannot, in fact, grow, Ralegh is making fun of Marlowe's idea that anything in nature can remain in a state of constant growth and fertility.
The flowers do fade, and wanton fieldsTo wayward winter reckoning yields; (9-10)
The alliteration of soft sounds like F and W usually creates a gentle tone, but here Ralegh creates the opposite effect by using soft sounds to deliver harsh content.